Originally Posted by
rankourabu
Don't know if they allow the specific fields, but it is very easy to apply your eupgrades (and keep your spot on the waitlist if needed) and change your accruing number afterwards for points crediting.
You've confirmed that actually keeps your spot on the list? I've never tried this with a waitlisted upgrade with anyone who has status (I've requested an upgrade for a nominee with their Aeroplan number, as is required, then switch them over to UA*nothing).
But certainly if you confirm the upgrade in advance, there's no risk of anything happening when you change it.
I can't see myself ever crediting an AC flight to not-AC, but if you find a willing agent, the command to add an AC FQTS would be something like: SR FQTS AC -AC123456789/P1