IS it OK to flash stock ROM from other country? Is it OK if I flash my phone with a stock ROM from another country? Wouldn't it have a negative effect?
Yes, it's OK to flash stock ROM from another country. BUT, take note that it may have different languages, and a different baseband/modem. Having a different baseband can cause network issues (or a very hot phone), but you can flash a baseband that works for your country.