If you have the character file, you should be able to do so, yes. In the bg1 multiplayer game, open the character sheet screen, press export button and save your multiplayer character. This will create the character file under your bg1 characters folder. Copy the file from there to bg2 characters folder. Open up bg2, start a new single player game and use import button to choose that file. That character is now your main in bg2. (Or if you want to create a multiplayer game, import that character into first slot. The character will be the star of the show now.)
On Ipad I get 'open in bg2' option when I save a character in bg1, so it is even easier.
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On Ipad I get 'open in bg2' option when I save a character in bg1, so it is even easier.