Hi
You can drive a UK RHD car in Macedonia, but you cannot register it here. Best bet is just keep insuring it in the UK with a Euro green card & you will be ok in my opinion. Technically speaking it should only be here 6 months of the year. You can register you car in Bulgaria & drive it in Macedonia, but you still have the 6month rule & from experience you will get stopped more by the Police with a BG reg. I drove a UK car here with no issues.
But overtaking can be more difficult with a RHD car in a LHD country, you can use a video camera to overcome that, or drive a vehicle that is higher up like a 4x4. Second hand cars here are extortionate compared with the UK prices & alot are clocked. So bring your car you will be OK.
Good luck
Cheers Martin