Well, if anyone really does feel the need to get rid of the ability to change the topic subject in a reply
Yep, thought of that, even implemented that hack for a while, but then you still got the issue of mixed subjects when you merge topics. And yes, you can add the code there too to sync subjects after the merge, but still.
Something in the codebase that just would look at post #1 would be my choice. Never got around to actually putting in a hack/mod myself