This is just a quick post because I couldnt find any info about this when i was looking.
I changed my region while there was less than 30 days left until my scheduled date and prometric didnt charge me. I only had to pay the $65 to ecfmg and request the region change. And then schedule a date with prometric once i got my new permit, and they didnt ask me for any extra fee's.
Note: I did however cancel my old appointment through prometric before applying for the region change. They didnt charge me then as well, even though there was less than 30 days...but from what i understood usually you have to call them and pay them $50 before you can usually reschedule a new date if you cancelled within the 30 days. However, after the region change i did NOT have to do that.