Custom thread msg for designated boards

[ChessMess]

I'm looking for a mod or method that would allow me to put a small message at the top of the first post in every thread for select board(s) within my forum. This would be useful for boards where you wish to convey a disclaimer but don't want to stick it in a sticky message that might be missed or ignored. It would need to be added to the message dynamically to ensure changes to the message are shown real time and editing of the message would not allow removal of the text.

Is there a mod that does this, or might someone with the skills find it of enough worth to create it?