Here are a few practical options/alternatives:
1. Put the mods on moderation who you don't want to post to locked topics. They can still upload their files, etc.
2. Have a hashtag called #Locked that you can put on topics where you want it to be very obvious they're locked, and instruct your mods not to post to those. Presumably they can read.
3. Create a new moderator permission called "Post to locked topics."
Messages are the sole opinion of the author, especially the fishy ones.