Flying on AA: Want to use AS perks but accrue AA miles?

[booyaa]

So I have Alaska MVP status and have a short trip on AA coming up. I want to use MVP status for free checked bags, better seats, etc., but I want to accrue miles to AA. I initially put down AS number on PNR, at what point do I switch it to AA and how? I can't even edit it now on AA.com. Call in after check in? Then change back to AS after arrival, and call in after return check in again?

Someone suggested to get gate agent to change it. Are AA gate agents well-versed in such a procedure? Is it important to have boarding pass re-printed at gate to show AA number?

Thanks

[Yaalili]

Gate agents can easily switch it. They will usually print a new pass automatically, but no need for it.