How can I prevent Steam validating workshop?

[Fiend]

Every few months, when I load up Steam, it will update a game and then decide to validate it.
This checks all files against the originals and replaces any that are different. Trouble is, I have a lot of mods, and with many mods I fix problems in them or adjust them to suit me better.
Validation wipes all of this out, so every time it validates, it takes about 20 minutes to complete the validation, then another 30 minutes to delete the workshop folder and restore from backup. Then pray that Steam doesn't decide to just validate it again.

How can I stop Steam from doing this?

[Nx Machina]

You cannot stop it because Steam is replacing the files overwritten by mods as it is checking the game install it knows about and not any modded content.

If you uninstall a game with workshop mods, those are not uninstalled because Steam only uninstalls the game, hence why people wonder why the free space they expect to get back does not match. The workshop folder has to be deleted or backed up.

[Fiend]

No, it is validating the workshop folder.
steam\steamapps\workshop\content\784150

Sometimes it validates the default game files as well, but today it only validated the downloaded workshop files.