Unfortunately there is nothing you can do to avoid Steam updates. You can always play in offline mode, but you can't install any new games. I create a new virtual drive for every Steam game. This means I have multiple steam virtual drives. So you could install Steam, install your game, update it and go offline. From then on, just play offline. If you want to install another game, just create a new virtual drive and install Steam again and the new game. Then follow the same steps to go offline. As long as those virtual drives with Steam never go online, you will still be able to play.