paste write this at 0x28F42 and change the last 4 bytes to the pointer to free space where you want to insert the hack in little endian.
Here for instance the hack is at 0xD0B000 so we OR 0x8000001 and flip it so that the lo byte comes first and the high order byte comes last IE ABCDEF -> EFCDAB
so here 0xD0B000 is written as 01 B0 D0 08
And paste this at the free space you desire
the implementation is simple, for half HP set the half HP weapon byte (3 in vanilla ROM, or 0xB if you applied Cam's status sword patch), and if you want Hell effect (current HP - 1) set the last unknown byte to 1 in nightmare along with the eclipse byte like so