If I use Steam's "uninstall" feature on a game, will it preserve custom content locally? I need ~50 extra gigabytes of hard drive space for a little while, and my vanilla Steam library is larger than that.

Well, my friend once uninstalled steam, and he had BEE on Portal 2. When he reinstalled it, BEE disappeared probably because of verified game cache on install, but the instances and custom content stayed.

FelixGriffin wrote:
If I use Steam's "uninstall" feature on a game, will it preserve custom content locally? I need ~50 extra gigabytes of hard drive space for a little while, and my vanilla Steam library is larger than that.

Yes... it will preserve all manually added content; after the uninstallation, only those folders you created with the content you filled them will be there. This also goes for the custom instances and maps you made in the sdk_content folder, in the case you want to uninstall the P2AT as well..