What is the likeliness of getting granted a transfer from my probation to transfer to a different county while fighting a case?

It DEPENDS on too many variables to list. What does your PO say?

Let me be sure I understand the question:

You were convicted of something previously, and are on probation. Now you are being prosecuted for some other offense (i.e.: you are "fighting a case".). Is this correct?

I don't see why transfer of probation would have anything to do with this new case. Are you desiring to move to the other county for some reason? What is the reason?

Why don't you ask your probation officer what you need to do to get the probation transferred?

Ask your PO for an application of transfer to a different jurisdiction. Its done all the time even between states.

What is the status of your PO. Is payments up to date, is any community service finished?

Fighting a new case, has no bearing on the transfer ( unless they are considering, revoking your probation)