Me and P2 on 2 separate booking LCY-AMS leave at 3PM, BA send me email few days ago said 3PM flight was cancelled and put us on 5PM, I log in today and was able to change mine to 1PM, but when try to change P2 looks like 1PM is full only option is 5PM

, I call Avios they said 5PM only have 1 seat for cash ticket, so can't change mine from 1PM to 5PM,
so just wondering Can BA overwrite Cash seats to reward seats? I know Aeroplan can now since they are on dynamic so every seats cash can buy can redeem for miles, but not sure for BA if it's worth escalating further?
Thanks!