I had 13 schedule changes last night. Clicked O.K. this morning on one award (3 seats) from LAS-SFO-NRT-BKK with a 1/2 hour time change btw LAS & SFO. Looked at it tonight and it's a CRJ200 from LAS toSFO. Called and gotter changed to a later A319 without any problem when I stated that my wife will not fly on a small plane. 1K agent said that since there was a change of time and aircraft no biggie.

But this was a very seasoned CSR agent who probably knew how to sell it to her supervisor, and knew the right reasons.
Don't know if it's done for everyone, especially once you agree to a change, but it worked for me tonight!

Give-em a call! Can't hurt, but have your new preferred flights handy when you call and politely request them by time and flight #'s.