I dunno...if he pled "guilty" the first time and has good grounds for wanting to change to a "not guilty" plea, like if he can show that his counsel advised him to plead guilty the first time and his counsel was incompetent, and/or he wanted to testify on his own behalf and his counsel advised him against it or something like that, then maybe he can.

I really don't know.

If he pled "not guilty", though, and wanted to change to a "guilty" plea, I can't imagine how that would be grounds for an appeal or a new trial.

Just speculating here, of course.