No your UPU application is processed like everyone else it's just that without rejecting USM's offer you don't know whether you have an offer from UPU or not since if you accept your name will most likely be removed from the UPU list but if you reject and have an offer from UPU than no problem it's just that you don't know whether you have an offer from UPU or not without first rejecting USM's offer. ^^"

if you got rejected by USM your UPU offer will go on like everybody else who never even applied to USM ^^