How can i assign a profilefield for just moderators only? As an example...moderators will be the only group who have a supportbutton in their topic/reply's.

Each moderator however, must have another image/button who points to his/her supportgroup
(php live) so forummembers can chat with the moderator of a forum wich he/she supports with this function.

I have copied the aim part of the ICQ hack and renamed it to this_sup with not an image but the code for one supportgroup. This has a profilefield but i had to make it functional in the CP, assign the right moderator to it and close it because others must not have this.
You can imagine that with more moderators this will make a very large public_topic.pl file and slow down the forum, and i have to make lots of profilefields.

Is there another way to do this?

have lib_posting check for mod status and add the link in for the topic page