Is too late to request that the mandatory part of my husband's plea deal be dismissed?

If he took a plea for 3 years, and that is not at all clear from your question, then the judge will not likely allow him to take his plea back. You can always change lawyers unless they are a public defender in which you need a good reason to ask for another lawyer. If he was going to lose the trial and get more jail time then he has no alternative except to stay with the plea deal.

Your question requires an attorney consultation. It is not a simple question that can be answered on this type of forum. There are many factors that would need to be considered and evaluated. I strongly suggest that you contact an experienced criminal defense attorney for a face-to-face consultation and give him/her all of the facts surrounding your husband's case. He/she would then be in a better position to analyze his case and advise you of his options.

It is possible to request a change of attorneys, ask the judge.

I don't understand the term mandatory plea deal. It sounds like he took a deal, but is still pending sentencing, and now wants to continue to negotiate the deal. This can be very difficult and, in fact, may be impossible at this point. He will probably need to move to withdraw his plea. He needs to talk to his lawyer about this. If his lawyer is court appointed and he wants a new one, he can ask the court for a Marsden hearing. Keep the following in mind: if he successfully withdraws his plea, prepare to take the case to trial. The DA is not going to serve up whatever he wants, in terms of a plea bargain, on a silver platter after he withdraws his a plea. Also, if his reason for asking for a new attorney is that he doesn't like the plea bargain, that will be insufficient for a judge to appoint a new attorney.