Gordon said:
Then the correct way is to use "Re: {whatever you changed it to} - WAS
xxxxxxxxxx."
Another format is:
Re: {whatever you changed it to} (was: {original subject})
The idea is to give the original Subject when you change it. However,
that is still rude. You are assuming that every NNTP client can
correctly organize the subthreads based on their References header.
That presumes the header is there. It wasn't long ago (don't know if
still a problem) where Google Groups would sort based on Subject. In
fact, some newsreaders have an option to fallback to sorting on the
Subject if the References header is missing or there is a problem in the
chain of message-ids in it.
Unless there is an extreme need to change the Subject, don't do it.
Also, regardless of using "was:" or not, you WERE replying so the "Re:"
prefix is still required - unless, of course, you want to pretend you
started the thread but then you would be condemning yourself as the
scammer. Changing the title does not preclude the use of "Re:" as you
were *not* the originating post for the thread.