Once a game is activated on a Steam account it can't be activated in another Steam account, it is locked to that Steam account. If you wish to install and play your games on a different computer then simply download Steam onto that computer, Login to your Steam account, then download the game.
How to stop a game from updating?
I went into offline mode to see if I could find a setting to stop Witcher from updating, but it seems to not be possible. When I click on the preferences for Witcher, the 'enable auto updates' dropdown can't be clicked. I logged in to see if maybe you could only do it online, but the game just started auto updating so fast, I had to log out quickly. Is there a way I can ensure the game doesn't update from offline mode? The reason I am doing this is because the new update screws up my mods, one of which is a huge combat overhaul that got taken down from the nexus and won't be updated. I'd like to at least finish the game with it.