Reducing the spawn rate of Archviles is not broken in itself. Reducing the spawn rate of Archviles by 100%, i.e., making them never spawn, this is very broken (unless making this happen is a real feat and a quest in itself); reducing the spawn rate of Archviles by 0%, i.e., not reducing their spawning rate at all, this is clearly broken in the other direction, it's useless. Somewhere in between (reducing their rate of appearance by 5%? 10%? Depends on how difficult it is to actually use the "DeHackEd" thing in the game) is a serviceable number.
I mean, what's the point of being able to mod weapons, since you can just give your chaingun +100 to damage and blatantly *ruin the game*? The answer is that of course you can't do that, because modding weapons was written into the game in a reasonable and balanced way. I wouldn't suggest anything if I didn't think it could also be made in a reasonable and a balanced way within the game.
Also calling it 5UP4 L337 H4X0RZ makes me wonder if you know what DeHackEd actually is--have you written Doom patch WADs before? It's used with some patch WADs that require more changes to the game than what can be done in a PWAD, so DeHackEd lets you make some changes to the Doom executable. It was a big part of playing and modding Doom at one point--maybe there are more roguelike players on this board than people who played a lot of Doom, I don't know, but DeHackEd is as much a part of Doom as anything that didn't come bundled with the game on purchase from Id could be.