I have a trip like this in the near future: SFO-ORD-XXX-ORD-SFO, and I am using two CR1's for upgrad. the first three flights are cleared, and the last one is waitinglisted. I want to get DEQM, so I plan to change my UA number to CO before boarding the first flight in SFO. I heard that if I do that, the whole itinerary will be changed to CO, not just the first one. Now suppose the last flight is still not cleared by then, can I change it back to CO in ORD, and still use that CR1 for the upgrade?