Add Parameter code fix can modify read-only documents

I ran the "Add parameter" refactoring, mistakingly thinking it did something differentt to what it does, and it tried to add the new parameter to all calls of the method. The problem is one of the calls came from the CLaSP source package, and it dutifuly modified the file on disk, which broke my build due to CS8300 (Merge conflict marker encountered), but when I try to go to the document to fix it, it's read only and I can't.