I am about to fly on DL with my sister who does not have status (I'm GM).
I called to request for her to be put on the companion upgrade list, but they needed a DL FF# for her, and she only has an Alaska #.

If she signs up for a Delta #, can she wait until the last moment when she knows she won't be upgraded and switch back to her Alaska # to earn the miles on Alaska?

If the answer to that question is yes, can she do it segment by segment or will she be switching her whole record back to Alaska, thereby losing her place on the companion UG list and having to go through the same routine for each segment?


(Yes, I realize the chance of a companion UG is small, but I figure we might as well try if it's not a ridiculous amount of hassle - which it might be depending on the answers to those two questions)