Join Date: May 1998
Location: Reno, NV (RNO)
Programs: AA LT Platinum, AS, UA Premier Silver, DL, HHonors Gold, Marriott LT Titanium, Hyatt, IHG Platinum
Posts: 4,723
I have tried many times in the past without success to use other AWD #'s. You must use the UA AWD # which is K019300. It doesn't matter much if you have enough UA certs to cover the entire rental, in which case you only pay taxes, but in your situation you will be stuck paying the higher UA rate. One free day still beats no free days!