Yes you can withdraw it. You can withdraw it at any time up to whenever the court before which the PCRA petition is active makes a decision and issues an order or opinion. That being said, before you withdraw a PCRA you should consult with your attorney, or if you don't have one, get one appointed or hired. If you withdraw a PCRA for what you believe is a good reason and it turns out to be not so good, you're stuck.
This is a bit confusing. By "granted" I assume the trial court agreed the defendant is entitled to a new trial. Having gotten what he asked for does he now prefer the original disposition? This question needs to be addressed to PCRA counsel.
A very unusual question. I can think of situations where one might want to withdraw a successful PCRA, but not very many. Please review your situation thoroughly with an attorney before you take any action on this.
I can see no reason to withdraw it. This can hurt you severely. Instead, it should be amended.
This is not intended as individual legal advice and there is no attorney client relationship established by this answer. It is advisable that you seek individualized legal assistance. This is not a substitute for hiring an attorney.