California Attorney General Opinion No. 00-205, 83 Ops.Cal.Atty.Gen. 136 provides:
But resort to the statutory procedure is not necessary either prior to commencing use of a new name, or afterward, for the purpose of rendering a prior name change valid. The statutory method for changing names does not repeal or displace the common law ability to change one’s name. (Code Civ. Proc., § 1279.5, subd. (a).) Accordingly, a person may change his or her name without legal proceedings simply by adopting another name and using it as his or her own. (In re Ross, supra, 8 Cal.2d at p. 609; Lee v. Superior Court (1992) 9 Cal.App.4th 510, 513-514; In re Ritchie, supra, 159 Cal.App.3d at pp. 1072-1074.)

California Civil Code section 22.2 provides:
“The common law of England, so far as it is not repugnant to or inconsistent with the Constitution of the United States, or the Constitution or laws of this State, is the rule of decision in all the courts of this State.”

California Code of Civil Procedure 1279.5 provides:
..nothing in this title shall be construed to abrogate the common law right of any person to change his or her name.

In re Ross, 8 Cal. 2d 608 - Cal: Supreme Court 1937 states:
[1] The common law recognizes the right to change one's personal name without the necessity of legal proceedings, and the purpose of the statutory procedure is simply to have, wherever possible, a record of the change. (Ray v. American Photo Player Co., 46 Cal.App. 311 [189 P. 130]; Smith v. United States Casualty Co., 197 N.Y. 420 [90 N.E. 947, 18 Ann. Cas. 701, 26 L.R.A. (N. S.) 1167].) Hence Mr. Ross may, regardless of the present petition, use the name of Keith if he desires.

In re Ritchie, 159 Cal. App. 3d 1070 - Cal: Court of Appeal, 1st Appellate Dist., 3rd Div. 1984 states:
(2) The common law recognizes the right of a person to change his name without the necessity of legal proceedings; the purpose of the statutory procedure is simply to have, wherever possible, the change recorded. (In re Ross (1937) 8 Cal.2d 608, 609 [67 P.2d 94, 110 A.L.R. 217]; Weathers v. Superior Court (1976) 54 Cal. App.3d 286, 288 [126 Cal. Rptr. 547].)
In so upholding the trial court's exercise of discretion in dismissing petitioner-appellant's petition, we do not depart from the long settled common law principle that a person may change his name without the necessity of legal proceedings (see In re Weingand, supra, 231 Cal. App.2d at p. 292, and In re Ross, supra, 8 Cal.2d at p. 609); we merely withhold our sanction. Petitioner is still free to call himself what he will.

Lee v. Superior Court, 9 Cal. App. 4th 510 - Cal: Court of Appeal, 2nd Appellate Dist., 6th Div. 1992 states:
Appellant has the common law right to use whatever name he chooses.

(3a) Appellant has a common law right to change his name to "Misteri Nigger" without the necessity of any legal proceeding. (4) A section 1276 proceeding provides a public record of the name change. (Weathers v. Superior Court (1976) 54 Cal. App.3d 286, 288 [126 Cal. Rptr. 547]; 4 Witkin, Summary of Cal. Law (9th ed. 1987) Personal Property, § 16, p. 20.)

*519 Since appellant's common law right to use the surname has not been abrogated (§ 1279.5), none of his First Amendment rights have been prejudiced.

In re Arnett, 56 Cal. Rptr. 3d 1 - Cal: Court of Appeal, 5th Appellate Dist. 2007 states in a footnote:
[3] Individuals in California retain a common-law right to change their names, in addition to the statutory right, by simply adopting another name and using it as their own. The statutory right provides a public record of the change, but such a record is not required to effectuate the change. (83 Ops.Cal.Atty.Gen. 136 (2000).)

In re Forchion, 198 Cal. App. 4th 1284 - Cal: Court of Appeal, 2nd Appellate Dist., 1st Div. 2011 states:
A. Common Law and Statutory Name Changes "The phrase `common law change of name' refers to the adoption and use of a name different from the one by which a person was formerly known, without resort to judicial process or other intervention by the state. The usage reflects the fact that at common law, all persons had, and in most common law jurisdictions including California, continue to have a right to change their given names and surnames at will. In modern times the phrase generally denotes the right of a person to use whatever name he or she chooses, as long as the purpose is not `to defraud or intentionally confuse.' ...
"In California, as in most American jurisdictions ..., a procedure has been established by statute (Code Civ. Proc., §§ 1275-1279.6) for the formal changing of one's name. The purpose of the statutory procedure is to have, wherever possible, an official record of the change.... But resort to the statutory procedure is not necessary either prior to commencing use of a new name, or afterward, for the purpose of rendering a prior name change valid. The statutory method for changing names does not repeal or displace the common law ability to change one's name. (Code Civ. Proc., § 1279.5, subd. (a).) Accordingly, a person may change his or her name without legal proceedings simply by adopting another name and using it as his or her own....
"The statutory procedure's very placement of the new name on the public record, however, unquestionably affords some advantages not bestowed on a common law name change standing alone. The statutory process provides an official document by which the change of name is definitely and specifically established and easily proved even after the death of all contemporaneous witnesses. Conversely, the inability to establish one's name for purposes of life's daily transactions, although perhaps only occasionally resulting when sole reliance is placed on the common law method, can be a substantial inconvenience when it occurs. Such are the circumstances in which one may be led to question the `validity' of a common law change of a name.
"A common law name change is `valid' notwithstanding the failure or refusal of others to recognize and rely on the new name. The validity of the 1306*1306 name change is unaffected by the refusal of others to accept it, simply because the validity of the change does not include a requirement that it be recognized or accepted by the world at large, or ... by anyone except the one who assumes it.... A common law name change, in other words, carries with it no mandate to those with whom one comes in contact to accept at face value the nexus between the new name and the individual who assumes it.
"Thus `validity,' for purposes of a common law name change, means that one has the freedom to change one's name and to use whatever name he or she chooses, qualified only by the proviso that the purpose not be dishonest. To change one's name by the common law method is to exercise the freedom to unbind oneself from the given name or surname acquired through birth or prior assumption, and to identify oneself anew; it is not to unilaterally impose recognition or acceptance of the newly chosen name as an obligation incumbent upon others." (83 Ops.Cal.Atty.Gen. 136, 136-138 (2000), citations & fn. omitted.)
(3) "The common law recognizes the right of a person to change his name without the necessity of legal proceedings; the purpose of the statutory procedure is simply to have, wherever possible, the change recorded.... While California case law seems to favor the legal change of a name to conform to usage, and while these cases uniformly teach us that there must be a substantial reason for the denial, they nonetheless recognize that the statute does vest the trial court with discretion in granting or denying an application for a name change. ([Code Civ. Proc.,] § 1278 ....) While it has been said that the trial court may properly deny the application if the name was adopted to defraud, intentionally confuse or intrude into someone's privacy ..., it is well settled that each case must be decided on its own facts, and that in adjudicating the issue additional reasons may also be considered." (In re Ritchie, supra, 159 Cal.App.3d at p. 1072, citations & fn. omitted.)
"[Code of Civil Procedure] [s]ection 1276 et seq. governs the process by which an individual can obtain a formal legal name change in California. The statute provides that, once a petition seeking a name change is filed, the superior court shall make an order setting forth the details of the petition and direct all persons interested in the matter `to appear before the court at a time and place specified ....'... The order directs that notice of the hearing and pending petition be published in a newspaper of general circulation. Section 1278 provides that if an objection is filed by any person, the court may examine `on oath' any persons `touching the petition or application' and `may' order the name change or dismiss the petition `as to the court may seem right and proper.' ([Code Civ. Proc.,] § 1278, subd. (a).) If no objection is filed with the court, the court `may, without hearing, enter the order that the change of name is granted.' ([Id.,] § 1278, subd. (a).) The word `may' is 1307*1307 construed as granting the superior court discretion in deciding whether to grant the petition." (In re Arnett (2007) 148 Cal.App.4th 654, 657-658 [56 Cal.Rptr.3d 1], citation & fn. omitted.) "We do not mean to suggest that the lower court must in every case grant a petition in proper form for change of name, but it is our view that some substantial reason must exist for the denial...." (In re Ross (1937) 8 Cal.2d 608, 610 [67 P.2d 94].)
"While the courts have a unique power to certify a name change, [Californians] still may refer to themselves by any name they like.... They may not [necessarily] demand that government agencies begin using their new names without a court order. This dual structure recognizes the reality that names serve multiple purposes, both private and public.... Among the private purposes are self-expression and identity, which are served by a person's ability to change one's name at will in social and informal settings.... Among the public purposes are identification and communication, which are served by the State's ability to tether one's name to a fixed identifier.... [¶] The modern tendency toward use of government-issued identification in both private and public settings may shrink the field governed by the common law, but both common law and statutory processes have long coexisted with respect to names, as they do in other fields of law." (Leone v. Commissioner, Indiana Bureau of Motor Vehicles (Ind. 2010) 933 N.E.2d 1244, 1254, citations omitted.)

Shelley v. Superior Court of San Diego County, Cal: Court of Appeal, 4th Appellate Dist., 1st Div. 2015 states:
[A] legal record of the name change is not required for a person to change his or her name, at common law

Affidavit