The reason I'm twitchy about doing it via direct balance changing is that it's hard for me to predict (since my original numbers weren't designed for it) where the result would end up on the boring vs. easy spectrum. There's a really, really thin line between the two.
That's what has me wondering if I might get a better result from nerfing AI / currency costs, at least as a first swing. It would still feel tense... but with less frequent / less expensive to recover errors, it would hopefully feel easier without wandering into boring?
On the other hand, if one of your reasons for wanting is this is you don't want Demon to require as much attention, this may be the opposite of what you're asking for.
I'll keep my thinking cap on about this, for now. I'll check out the branch you linked sometime, I should have known mainline DCSS wouldn't add difficulty levels, but then again, I haven't understood many of the things they've done in the last couple of years.