Hi,
The COP is driven by CPMUCOP register.
In special mode, you may write CPMUCOP register without restriction. Any write will restart COP timeout period.
In normal mode, you may write CPMUCOP register just once. If bootloader writes CR[2:0] as “000”, the application cannot change it without MCU restart.

Please check the complete CPMUCOP write conditions in RM.
I hope it helps you.
Have a great day,
Radek