I believe FPROT is not user writable (at least not in all MCU derivatives, don't know about the specific MCU mentioned). FPROT becomes loaded automatically with NVPROT which is always in protected space if you have protected the bootloader, above any code. So, I don't see how this would work.To answer OP, FPROT register can be written to increase the size of protected flash. You bootloader may have NV write protection register set to protect just the bootloader. Then just before bootloader jumps to application code, or in applications startup, there could be a write to FPROT to protect whole flash or whole flash minus flash data area.
4.7.4 Flash Protection Register (FPROT and NVPROT)
During reset, the contents of the nonvolatile location NVPROT is copied from flash into FPROT. This
register may be read at any time, but user program writes have no meaning or effect. Background debug
commands can write to FPROT.
So, sadly I cannot manipulate the FPROT register. That said, the code will be very 'tight' regarding erasing and writing the flash, and the RAM routine will be refreshed each time I run the flash routines.
Are there any other issues? Will the LVI mechanism prevent the chip from shooting its foot off in case of a power fail? This should be very unlikely, as the app monitors the raw power supply and can stop the flash routines long before we have a power problem.
Thanks!
Bob