Hi Sid,
Thanks for your answer.
1) Ok, great.
2) That makes sense to me (or to my board, to be more accurate). In fact, it belongs to me to decide what prefix to set before thread title. It would be a way to define a thread "in course", "solved", "important", etc...
3) Humm... after would have been better...
4) (And finally...

) I would need all these prefixed thread (or some of them, by type), to be pinned at the top of the forumhome (plus to their own forum). I thought I've seen a board somewhere which had such feature... but I don't remember where...
I'm going to see your add-on,
Thank you anyway.