You can edit anything with a hex editor, however the question is would you want to? The answer in this case is depends what you want to do but probably not.
A full tweak and remaster would be horrible to do with one.
Some basic tweaks are more doable -- if there is only a couple of notes you want changed to something else or maybe a slight timing change for things.
In any case you would first want/have to spend a considerable amount of time pulling the game's sound engine apart with emulators and disassemblers. Once you have that you would probably want to make a program to handle it, or at the very least a kind of spreadsheet to take some of the tedious manual calculations out of the equation.
Some later consoles have more commonly used defined sound systems but most things 16 bit and older are a pretty custom affair, and will also see you wanting to know hardware.
Topic: How Do I Edit/ Replace the Sound Files in an NES ROM? (Read 3960 times)