I'm just doing a "modernization" patch of my own, updating names, exp/gold gain, shop costs, etc. But a few values (Metal Slime, Gold Golem) would ideally go over the 255 limit.
I'm a bit confused: are you saying you want to set those enemies to give you more than 255? Because the game code doesn't support that. Open FCEUX and set an execute breakpoint for $EA0A, and you'll see that the game stores one byte for the XP total to $00, and stores zero to $01. But if you change $00 and $01 to FF, you'll get 65,535, so it's clearly possible to get more than 255 from an encounter. The problem is, the game ignores the most significant byte when loading the XP total, so if the enemy is 144 normally and doubled, you only get 32 (because 256 is ignored). Of course I could change the routine so that the carry flag is also considered, which would solve the problem.
Anyway, time for an update!

Thanks to KingMike's assistance, I've made an update to my Final Fantasy 6 (SNES) patch! Now when you get later in the game and earn Magic Points for your Esper stuff, you'll earn double. I'd never have been able to do it without someone providing me with a late-in-the-game save file, so big thanks to KingMike for stepping up!

Also in the pack is Dragon Quest 3 (SNES), which complements my previous patches for DW3 on GBC and NES. I think I may have to take another look at my DW3 NES patch, since it was one of the first ones I did and I want to make sure it's okay, given what I've been learning since then.
http://s346165667.websitehome.co.uk/psyktrans/2xp-20180114.zipI've now reached the point where I think I'll officially release a few patches. I've now completed Dragon Warrior/Quest 1 and 2 on NES, SNES and GBC, so I know the patches work correctly.
Also, when you reach the last shrine before the final castle in DW2, FAQs will sensibly recommend that you reach level 30 before trying. Well, I made it there in the 20s and really couldn't be bothered to grind at that stage, even with double XP. So I used my hacking skills to make Game Genie codes that will give you super XP from a battle, then turned them off when I was up to the level I wanted.

And I'll share them with you now!
On Dragon Warrior 2 (NES), there's an internal check to allow you to earn no more than 9,999 XP from any battle, even though there isn't a single battle in the game that could earn you anything close to that. So I just replaced the branch instruction with one that does the opposite (ie load 9,999 XP if you get LESS than that, not MORE).
EUSPEPEP - gives 9,999 XP for every fight
Of course, if 9,999 isn't enough, you can use these two codes to change 9,999 to the maximum of 65,535.
NNSOKOYE + NNVPOPYX - gives 65,535 XP for every fight (with EUSPEPEP)
(for testing purposes, I used just the first patch to play through the entire game from scratch.

It didn't take nearly as long, obviously)
For the Game Boy Color version, I've also made a Game Genie code, but this one always gives you 65,535 XP. The GBC version also includes a maximum routine, so this code replaces the jump instruction with a load instruction, meaning the code just continues to load the maximum into the XP total.
26D-67B-2AA - gives 65,535 XP for every fight
As for the SNES version, I used Pro Action Replay to patch the RAM, whereas Game Genie patches the ROM. It just puts 255 in $7E0ED9, which is where the most significant byte of the XP total is kept. Therefore, you always earn a MINIMUM of 65,535 for each fight, as well as adding the least significant byte.
7E0ED9FF - gives minimum 65,535 XP for every fight
Have fun with the patches, and the codes!
