Return ticket (crediting outbound to BA and inbound to QF)
 

I recently flew QF to MEL from JNB (via SYD). I entered my BA Exec Club number into the booking and am awaiting the miles to be credited for the two flights. Tomorrow, I fly to PER from MEL on QF as part of the same ticket. I would like the miles for this flight to be credited to my QF account instead.

If I swap from my BA number to my QF membership number at check in, what is the risk it will retrospectively end up crediting my previous flights to QF as well?

If there is much risk, I won't take it as BA is my primary account but every now an then I credit the odd flight to my QF account as I am nearing QF Lifetime Gold (OW Sapphire), so I think I may as well get to that as I clear BA GGL each year so it won't reduce my status with BA.

Any advice very welcome.

No reason it should not work. Keep your boarding passes with the respective FF account references until everything has credited the way you want it to.

Historically (for me), the only times this has been an issue has been with connecting / same-day flights. It can be done correctly but requires data entry for each flight segment rather than the PNR.

Happy wandering
Fred