An update here in case it's helpful for anyone.

I had two one-ways booked with AS miles and I texted AS to switch my AS number to my AA number (given I have Platinum Pro with AA and nothing with AS). Agent was able to successfully change to AA number for both reservations. A couple of quirks / things to notice though.

For flight 1:
- During OLCI it appeared as if I had no FF number attached to the reservation at all, and trying to input my AA number resulted in an error message like "FF number not found." I continued OLCI anyways with no number
- Boarding pass was issued, with 1) the correct boarding priority (Group A), and 2) correctly on the waitlist for F, however no mention of oneworld Emerald anywhere on the boarding pass, or any indication of the FF number
- Around T-20, I got an "upgrade" to Premium Class
- At the airport, self-checking in correctly gave a free bag allowance

For flight 2:
- I was able to select a Premium Class seat ahead of time
- During OLCI, still no indication that I had a FF number attached, but based on experiences with flight 1 I proceeded anyways
- Boarding pass was issued, with everything looking correct (boarding priority, on waitlist for F), but this time oneworld Emerald was denoted
- Around T-13 I received an upgrade to F
- At the airport, free bag allowance was recognized

So.... TLDR: on an AS award ticket you can switch your AS # to another FF number by having a rez agent change it, though it seems to be buggy, but at least all of the benefits are recognized.