(oops lol - just realised that the "perl -p -e ... " at the end of the OP is an effort to solve - first impression was it was just a monk signature)

... try to match as closely as you can to the substring you are trying to change - use /...$/ to mark the end of the line in your regex - match line by line and if there are variations, if necessary, be prepared to use multiple regexes for them.

See also perlre