Hi Denis,
I recently faced this problem as FCA and BCA are appended as defined in IAR, External Flash has Two ranges A and B or( QSPI A and QSPI B) where you can map these as two independent application, but a jump to the other can only be possible if its been hard-coded.
As entry point change will require changes in VCTOR register of SCB of arm(To Remap Interrrupt Vector Table).
It depends what type of requirement you have in hand.
In my case I used a Second Stage Bootloader to move entry points in FCA and BCA region, as initial FCA and BCA region are required during initial boot only, a Second Stage Loader/Application can update Them.
Best Regards
Saurabh Saxena