The OP was asking about a permanent linkage (between two OW accounts, one with status and one without), as AFAIK there is none.

The post above details how to do it (change FF program at check-in) for a paid flight. (You buy the flight using the FF program you have status with, then at check-in change to the FF program you want to earn with.)

I still don't understand how/if I can use my OW status benefits if I book using miles from a OW partner where I don't have status. (In particular, I have EXP now and lifetime PLT status at AA, but no status while a lot of miles over at BA, and with Avios new scheme, for short intra-US flights, BA miles may sometimes make more sense than AA miles. But how do I get priority check-in, priority boarding, etc, if my BA account with which I book the award flight on AA and my AA account that has the status aren't linked? (And I'm not aware of a feature on ba.com where I can specify another OW account while booking a flight using BA miles.)