Short stripper,
Can’t speak specifically for Bulgaria, but I have done this twice with different EASA authorities.
Just before Brexit I went to work in Spain and converted my then UK license to AESA, It was a fairly straightforward process. First I was required to do some dual time to the point where I could pass the SEP skills test , in fact most of that was covered doing famil flights around Madrid. I then flew and passed the skills test {same as for PPL renewal} note that these days EASA require an instructor to validate you prior to the test, but this can be done via ATO or an independent FI who flies the dual time with you.
To satisfy the exam requirements I had to write to CAA to transfer my file.. It turned out that since my original UK PPL was the old ‘poo brown’ version of the UK PPL that i had not sat and passed Human Perf and limitations exam , so I was required to sit and pass that exam along with EASA Air Law, both straightforward and could be done in English.
For the Medical I just renewed in Spain and transferred all my files since it was easier to do so. However I have recently had to repeat the entire process for my French license !
The requirements are the easy part, the admin however does not always go so smoothly ! Good luck….. as always its worth it in the end.