Creator doesnt like code diving because he created a free and a huge and a hard game for past several years of his real life; and instead of playing to finish it, we try our hardest to cheat in it.
Creator knew that his game will be dissected by a large community, and everyone will share info and tips and exploits in between themselves. The thing that Creator did was to create an overly complex game with too many features and possibilities, in the way so that a GB is a neccessity. In other words, game was made suitable for a community, not single players. Guidebook is a good thingy, but Creator had to know that the GB writer cannot offer people observations and thoughts, but exact data. Which gets obtained from code diving. ADOM GB is already pretty-much complete, and available to people. It's unfair to ban it and remove it from The Internets, because people who literally know the whole GB (like me) will have a complete advantage over those newbies who potentially wont have access to GB anymore.
I took a look at a plenty of executables, and they're fun to look at, and that's how I sometimes satiate my programmer spirit. At times, exe can also be altered to gain benefites, but in games, we call that phenomenon 'cheating'. I have read somewhere that ADOM has all the textual data in plain text (go look, or dont. i dont care). One pretty interesting use for diving would be to alter the text to your needs (meaning, supressing the 'cursed' and 'blessed' messages, as they are already colourcoded in your inventory; also to suppress some overly long names and messages into something more readable) which actually sounds extremely tempting to me, since I play MUDs; in a MUD, you can usually colour any text into any colour you want, and substitute it with text of your choice, which always makes for an easier experience and less 'more' prompts and less eye strain.
Altering some of these messages is a minor neccessity, but altering dice is cheating. Do it at your own risk, and keep it private. If it makes the game nicer for you, go for it. But no one will want to hear about your heroic conquests, where your main equip was a mutated (+99,9d9+99) dagger, or where wands of wishing were made as common as wands of light.
Enjoy.