Easy is relative. I’m pretty sure the easy way is if the game developer creates a separate “beta” branch. The other way is to turn off auto-update, manually download depos and extract them into the same folder essentially reinstalling the entire game with the updates you want and then putting them in the right steam folder. I personally wouldn’t call it easy. I’d say it’s tedious, prone to user error and unnecessarily time consuming.

It would be easy if Valve took their “beta” branch feature and expanded it to be an actual rollback.