I've not yet worked directly with rewrites for Classifieds, so I can't give you a specific answer, though the DBSEO Mod does work with Classified to allow for rewriting the URLs. It might be that if the other mod doesn't do what you need that Fillip H. could provide some pointers for you. He's the rewrite wizard...
Regarding your other question, I'm not sure if you are wanting to remove it so that it never appears or you are having problems getting it to clear?