To be able to add my friend in Starcraft 2 who is in SEA region I too have to be in SEA region I presume. When I tried switching to SEA region it required me to enter my character name. My question is if i enter my character name will I still me able to have my levels and acheivements still with me?
Achievements and experience are specific to your region, so when you (essentially) make a new account on SEA, the account will be empty.
The creation process on SEA will be as if you just bought the game and are entering your battlenet username for the first time.