Apparently they’ve been somewhat inconsistent with that. From what I’ve read, deleted comments have been more likely to be restored than edited comments, though either have been reported to have been messed with resp. left alone by Reddit.
I for one have replaced most of my posts with a “I hope u/spez grows tastebuds on his rectum” standard text some three weeks ago, which they appear to have left alone so far. But that’s a sample size of one user so by no means representative.