Thanks, this was so easy, yet so confusing, any other game Ive played like this from steam always swapped the entire account if someone else used the computer (logged in as them). Now I can have LAN games without requiring people to bring their computers first.

Edit: spelling.

I have found if I lend my computer to a friend to play at my house with, and they log in to steam (we both own Factorio) that if we choose to play multiplayer it will not let me in as it has my name on both computer in the game, making impromptu game sessions impossible. it says (name of player) is ...