nes prg-rom space is:



 bank0 - $8000 to $BFFF

 bank1 - $C000 to $FFFF



smaller switchable banks are possible, just depends on the mapper. ram is

located at $0000 to $07FF and is thus mirrored after that up to $2000.  all

code/data is loaded into those 2 banks of prg-rom, though thats not there actual

offset in the rom. the value will be stored in ram when needed but will first need

to be loaded from rom. you need to find where in rom it is loaded from by using a

breakpoint set to when that location in ram is written to. and ram will be written to

like so:



   lda #n

   sta $g



where n = the value of health and g = offset in ram. though it might be tricky

because indirect or indexed addressing might be used or they will use the X or Y

register instead of the accumulator (A register). so you might get something like:



   lda ($nn), Y

        or

   lda ($nn, X)



which are the two forms of indirect addressing (X and Y are 6502 registers, nn =

zero page address). or you might also get one of these:



   lda $nn, X

   lda $nnnn, X

   lda $nnnn, Y



which are forms of indexed addressing. ($nn = zero page address and $nnnn =

non-zero page address) when the game stores the value into ram it may also use

indirect/indexed addressing rather than absolute.