What is the test for vacating and modifying a sentence in a criminal case?

" 'Where the trial court relinquishes custody of a defendant, it also loses jurisdiction over that defendant. [Citation.] If, however, the trial court "retains in itself the actual or constructive custody of the defendant and the execution of . . . sentence has not begun," the court may vacate and modify the sentence. [Citations.]' (People v. Karaman [(1992)] 4 Cal.4th [335,] 344.) [] 'In a criminal case, the execution of a judgment of conviction is the process of carrying the judgment into effect. [Citation.] [Fn. omitted.]' (People v. Karaman, supra, 4 Cal.4th at p. 344.)" (Cornelius, supra, 31 Cal.App.4th at p. 347.)