Is a motion to enter a plea of not guilty by reason of insanity reviewed for abuse of discretion?

Denial of a motion to enter a plea of not guilty by reason of insanity is reviewed for abuse of discretion. (People v. Montiel (1985) 39 Cal.3d 910, 922-923 (Montiel).) A criminal defendant is permitted to change a plea to "not guilty by reason of insanity" prior to trial "for good cause shown," pursuant to section 1016, subdivision (6): "A defendant who does not plead guilty may enter one or more of the other pleas. A defendant who does not plead not guilty by reason of insanity shall be conclusively presumed to have been sane at the time of the commission of the offense charged; provided, that the court may for good cause shown allow a change of plea at any time before the commencement of the trial. A defendant who pleads not guilty by reason of insanity, without also pleading not guilty, thereby admits the commission of the offense charged."