Update on region conversion...part 2
I have tried full firmware conversion using SD card method, using Ldr.bin, 0E.bin and 7F.bin extracted from EU firmware but ended up with device stuck on logo with message above logo "System Software Missing". Even when I pulled out the SD card, problem stayed the same. I think that was the case because in update.txt, on SD card, first line was "del,0:/.System/gupdate.gcd" so it probably deleted old FW but for some reason couldnt load the one from the SD card. In that moment I thought that I bricked the device and that it will be the same case our colleague @gigidel had with his Motorrad VI, but either way I wanted to try loading FW using WebUpdater.

So, loaded EU FW in RGN tool, saved it as .rgn file, used webupdater to load it in pre-boot mode and everything went well. After restart, I selected "Other" region among many other offered (not just US, China and Taiwan as was previously) and I was able to select my language in text option of the device. In Device info and GarminDevice.xml, software version was 350 (correct EU version) and HWID was 1541 (correct EU hwid). Garmin Express recognized the device and offered me an update of text files and also, interestingly, Chinese map that was previously on the device. Maybe because the Device ID was still the same, I dont know...
Nevertheless, after putting the EU maps, I can confirm that everything is working fine.
Couldnt do it without you @Neil.