Borderlands – How to connect Borderlands 2 Mac and PC through LAN

From the main menu, go to Matchmaking->Match Browser. There, in the bottom right corner of the dialog, will be your game version, like 1.4.0.

Copying the save file should be sufficient to copy your character to another computer, but I'd be suspicious that the file has some sort of ID to identify the character -- logging into one game with the same ID from two computers could be a problem.

I don't know that this ID is present, but I'd expect one to be there.

1) So, to answer your first question, IDK, but my gut says probably not possible to play the same character twice in one game.

2) No, moving the files around shouldn't cause an issue with playing online. I've used a save game editor to create characters - I play through Steam even - and didn't have any issues using the editor-created character single player or online.

Maybe you could rebuild a character to the point that you were at if you have issues?

This is the editor I've used: http://blog.gib.me/2013/04/18/borderlands-2-save-editor-revision-155/