I'd been playing and editing the mod for a few weeks, when I realised that it wasn't going on the right way.
I had to rise the monster levels, to ensure that the XP gain would be proportinal to the player's level, when above 99. By doing that, they ended up having much more power, mainly HP.
The result was: a fair normal game, a hard nightmare game, and an almost impossible hell game. So, I had to edit the file which has all the monster levels characteristics.
After that, I made a sequence to continue their characteristics by multiplying each one by a number, resultant of a comparison I'd estabilished. This had worked a little, but not enough.
So, I realised that the game was not made for levels above 99. Really. At least, not a level like 255, as I desired. There're no items, nor prefixes/sufixes, and balancing everything would really be hard.
Then, I had an idea: I'd have to start almost everything again, from the beggining. Mainly, reducing the maximum level (maybe to 120, no more than it), giving to each level 5 stat points (maybe 6 or 7) and 2 skill points per level. I think it'd be enough to reach what I've desired, and end up almost as it'd end in the current mod situation, without the need of balancing the monster.
But I'm not sure. It'd be risky, as I actually don't have much motivation to keep working on it, and mostly, testing it, as it takes a lot of time and is somewhat repetitive.
That's all I can say for now. Just though I should share the situation with everyone, even though I believe no one else cares about it... lol.