If you have any problems, you can always restore your ARCs from the backup copy you made earlier. Don't forget to save copies of your changes that you really like to: having checkpoint backups saves a lot of time and frustration.

If you forgot to make a backup copy, you can repair your build using Steam. Go to Library : Home. Go to the Marvel vs Capcom Fighting Collection entry. On the same line where it says "Play", there is a gear near the right side. Click Manage : Properties... . Go to "Installed Files". Click "Verify integrity of game files": that will have Steam restore the original files.