NES Help with NES rom modifying?

[Prototype Squid]

How do I modify an NES rom? Huge Mother fan, I am hoping to make a modified version of Mother 25th Anniversary Edition that retains all the changes made in that version but just fixes the broken encounter rate, the STATUS stat name, and Giegue's name. I want to keep the same stat growth and party starting levels, so re-faithful isn't what I'm after.

 

[AnonymousCookieMonster]

If none of the data changes size, hex editing may be an option, finding the appropriate name(s) and just editing would work.

The encounter rate on the other hand, either the game data's value of what threshold is the RNG, which is either going to be game-wide or going to be area specific, or monster specific. That sounds like a lot of complicated work depending on how it's done. If there's someone who modified the encounter rate already, comparing before/after would be the easiest thing to do.