Many thanks to everyone who provided recent DPs on this, which helped me to pull the trigger. Here's my DP (so far) for
Platinum:- 12/23: Switched airline to UA on AMEX via chat. I had already used a small amount of the credit for this year, and the auto-responses on the chat said I could not change airlines for this reason - but when I got a live representative, he said he would do a one-time courtesy change. Super easy!
- 12/24: Made two $100 TravelBank travel cash purchases in two transactions. Currently shows as two "United Electronic Ticketng" pending items on AMEX.
Will report back after finding out what happens next. Thanks again!