I already have Company of Heroes on Steam. Since the game is switching over to Steamworks for its multiplayer component sometime in May, a "New Steam Version" of the game has appeared beside the original.
Unfortunately when I try to install it Steam appears to require me to reinstall the game
Is there any way I can avoid having to download 9GB of game data all over again?
Best Answer
Start downloading the new game until the folder structure got created, then stop Steam. Now simply copy the game folder to the new location. Start Steam again and it will download everything that does not match.
I'm not aware of any other way, so if this does not work you'll probably be left with no choice other than to download it again.
Note that Steam at times acts intelligently and uses identical existing files from other games, though that is very rarely the case and, judging from your question, not the case here.