They're not going to do that, especially over a very simple trim piece replacement.
I'd bet the OP could buy the part for a couple of dozen bucks and put it in without any problem. Not that s/he should have to, but they probably could.
My last used vehicle needed a replacement antenna that they promised to do. I bought a new part on eBay (OEM) but the dealer's service department couldn't ever work out a time for me to get in and get it done. I went to the more local dealer and they put it in for me. Total cost on my end...$130...and the selling dealer reimbursed me in full. This OP sounds like, well let's just say "a difficult customer".