Can you bypass the space requirement when manually restoring backup of Steam game?

Solution 1:

If you backup/restore all of the correct files (including correct appmanifest_######.acf file), then restarting steam should make it re-check your library and add the installed games.

I tested it myself just now:
1) I moved the game folder (absolute drift, due to small size) (from steamapps\common) and the appmanifest_320140.acf file (from steamapps\) outside of steam folder
2) uninstalled the game from within steam
3) restarted steam to make sure the game stayed uninstalled
4) moved the game files and appmanifest file back into steam library
5) restarted steam and it immediately added the game to the library as ready to play

You can find the game ID (which is the ###### in the appmanifest_######.acf file) by going to the game's store page on steam and checking the URL. It should be http://store.steampowered.com/app/######/ (the ###### being a number representing the game ID). So, for example, the game Absolute Drift has the game ID 320140, therefore I used the manifest file with the name appmanifest_320140.acf