>>17448211It was basically blind hex editing.
It was a pass through between the cartridge and the system and you would enter memory addresses and hex values to replace them with and if you found the right one (or read it out of a magazine) you could overwrite variables like how many lives Mario has, how many HP Zelda has, how much cum you have left in metal gear, kind of like a universal trainer but to actually find unpublished codes you would need an unbelievable level of both autism and luck.
Fortunately it came with a code book and magazines would publish new codes that were found.