yep have a look in the example of the code i have posted in the examples , but hendrik is correct the large bulk and sectors erase options suck for a byte change when the location has been written before

even with this routine its a time pain but Flash are large chips/cheep and if time is a worry then sram /eeproms are probably a option better suited , but there are time when only a few bytes changed option is very nice to have on flash chip

i am thinking maybe 2 x for, next loop based on the selected location for the change , eg , if selected page/byte is x then copy data to x-1 , and next loop x +1 , this is then done for lower address to lentght of data changed then set upper address