Well it's cool that you've had a look at it, it's quite bad in that one.
Interesting, I'll check it out. I had the impression that it was usually fairly simple to change, since a code was made for the Mega Drive Double Dragon port.
It is not difficult in the same way some hacks make for changes that have all sorts of odd effects within the game and you have to hunt down and change each one.
It is not difficult in the same way some hacks need say a fair bit of text compressed and inserted back and the hacker then gets to hunt down space and crowbar it in where they can, or otherwise having your code running on the ragged edge of possibility if you have to get in within a vblank loop.
Equally it is not something one can possibly do the hacking for and palm off to someone else -- I build a text extractor and inserter, or same for a sprites or music, and I can then wander off and let whatever more linguistically or artistically inclined person do whatever they feel like doing and probably not even have to bother me.
It is more that
Say you have a game that keeps your character in the middle of the screen all the time. Enemies come in and owing to sprite sizes and speed you might have an unreasonable quarter of a second to react, with a bounding box such that you can be three quarters of the screen away and thus say a more reasonable reaction timeframe (such a thing could fundamentally alter a game, no argument there at all, possibly far better than instead slowing things down which could be another solution).
Trouble is you now have to define a bounding box (if bounding box does not make much sense think instead like a dead zone in a joystick) for a game which never had even the notion of such a thing; if you have ever seen a widescreen hack and the enemy only starts operating when the normal standard width kicks in then something similar could apply here. You then get to possibly sort this out, which might be harder if the original devs could quite rightly assume the player is always going to be in the middle.
If the game already has a bounding box then you might be able to pump up the size of it, or maybe change it for one of the other styles mentioned, or maybe set the player's normal position three quarters of the screen length from the right (assuming standard left-right scrolling game). Though changing location might trouble things if you are prone to being attacked from both sides.