Message got eaten by the forum, so I try again ...
EEPROM simulation usually goes under the term IAP (In-Application Programming). Perhaps there are SDK examples or application notes for your MCU.
First, you would need to reserve a Flash sector of appropriate size, or else the linker would use it for code or variables. This means removing it from the linker script. The most upper sectors are usually preferred, for obvious reasons.
But IAP has it's downsides.
First, Flash can only be erased as whole sectors, not single entries (bytes/words). Writing is usually done in word or longword unit, though.
Second problem is timing. Most MCUs have only single-bank Flash, i.e. all Flash sectors share one erase/program logic and voltage generator. This means, no code execution is possible during erase/write, your application will stall. This might get you into trouble with externally driven interrupts or realtime tasks.
Third issue is endurance. Most vendors guarantee 10k or 100k erase/program cycle for their Flash.
This number is valid for the worst-case temperature. If you erase/write rarely (less than once per hour), this will probably not be an issue.
I have no specific experience with the LPC55Sxx MCUs itself, though.
First step would be to check the datasheet and user manual for the Flash memory map, and Flash parameters.
IMHO, adding a serial EEPROM or MRAM device would be much quicker, and less troublesome.
