I've ascended every class except Rogue and Healer (and neither are really more challenging than Tourist, I just never got to it) over the last ~10 years of idle playing of NetHack 3.4. NetHack is not quite a solvable game, but there are fewer patterns that matter, at high-level play, than one might think. Once you are able to see those patterns (many of which are just part of your standard ascension kit) as part of the game, the solutions generally become fairly obvious and you can just drill through it.

You definitely won't win every time, of course, but you'll be pretty okay.

I've ascended without modifying code. I did have to insert a level map from a game in explore mode because there was a bug in the version I was playing. The bug meant that there was a level where there was no up staircase generated.