www.makemkv.com

For this setting i assume it just allows the movie to play in vlc without damaging anything in the file.

My question is this..

If you scanned a movie without it and wanted it do you need to rescan or can it be added after the fact somehow?

Are you talking about VLC on the integration tab of MakeMKV preferences?

Yep! Thats the one.

That integration enables VLC to use MakeMKV as the decryption engine to allow VLC to play discs.

If you've used MakeMKV to rip a disc and create a .mkv file, the copy protection that comes on discs has already been removed and VLC can play it on its own.