If you are looking for hex-editor, I can recommend XVI32, I am using it myself.

Decided to test the Paladin with cheats enabled.

Lay Hands doesn't recover just by resting. If you are at full health, the game won't let you rest to recover this ability, which can be extremely annoying.

Contrary to what the manual says, Paladins get all Cleric spells up to 4th level. However, their Spiritual Hammers only go up to +2 (reached at level 15).

Level cap is 20 for Human Paladins.

The XP cheat only seems to give 50,000 XP at a time, so after a while it took 6 'X' presses per level gained.

As a side note, with maxed enemy difficulty and frequency, I would expect a single class character to reach the level cap around dungeon level 10.

12th floor is another easy floor.

Of note, my mage level has maxed out.

For high XP dungeons (max enemy frequency and strength), I recommend making the dungeon around 10 to 15 levels long. Anymore and you will cap your level and have no way to improve for the rest of the dungeon.

After a certain point new gear doesn't cut it anymore. I'm running around on floor 20. It's been ages since I've maxed out my fighter/mage/cleric. I'm under the effects of

protection from evil
aid
resist fire
resist cold
magical vestment
prayer
true seeing
haste
improved invisibility
Ilyykur's mantle

Nothing can touch me and I kill almost everything in the first round. So yes, I guess I made my dungeon too deep.

SPOILERS ahead!

Analyzing game files, looks like the most rewarding and powerful opponent is Balor Tanar'ri, who gives 46,000 EXP (in comparison, Elemental Lord, who is final boss iirc, gives "only" 30,000 EXP).

On other side, it seems that game isn't entirely faithful to manuals. Scaladars seem to reward 10,000 EXP instead of 5,000, Wraith's Movement seems to be 12, instead of 9, etc. I can't find how game keeps HD, AC and damage stored. I think I found THAC0 but it differs from manual as well...

Anyone knows if there were some kind of modding tools made for Dungeon Hack/Eye of Beholder?
Some gear pieces seem to be quite rare. I found "Shield of Keign +1" and not even any other piece of the set (or any other set).

In my current run I have plate armor of Keign +3 and sword of Keign +2.

As far as I'm aware there are 8 sets of equipment in the game. I'm wearing the armor, but by now I have better weapons. Some sets grant bonuses, if you equip all of it's pieces. This one would grant a small amount of magic resistance.

Thank you dtgreene and Sarisio for the hex editor tips. :)

Floor 13, nothing dangerous other than the spellcasting boss. (Normal enemies are Shambling Mounds and Grave Mists.) I haven't been bothering to put all my spells up. (Do Bless, Aid, and Heroes' Feast stack?)

Found Maul of the Titans, but apparently 19 Strength isn't enough to use it? (22, which I can get with gauntlets, is.)

One of these times, I may play a Cleric/Mage (no Fighter) with average Strength and my "hack new spell at each level" rule, along with the rule that armor that prevents mage casting can't be worn. The idea is that I want a playthrough where offensive magic is available and worth using. (Magic power on High, of course.)

I love the hack in Dungeon Hack. Melee is my main playstyle and magic for identifying and ranged as a backup attack against some monsters that are dangerous in close combat. If I don't have much ranged magic attack items that do make up for it.
Heck I've even played pure mages as mostly melee characters. :)
Oh and I mostly play it on kinda normal. I up the monster and food items numbers usually.

I am thinking of starting a new game of Dungeon Hack, this time as a Ranger/Cleric in a dungeon with some puzzle and trap elements and only 15 levels. (My old character is in the middle of the 13th level of a 25 level dungeon and is nearly maxed level wise.)

This way, I don't have to worry about mage spells, but item identification will get a little harder.

My third playthrough (since getting the game again) may be the Cleric/Mage with my house rule and little treasure.

I am thinking of turning off undead this second time around because I would like to see more non-undead and not deal with level draining. (Of course, there's still the Cockatrice monster...)

First Floor as a Ranger Cleric:

No Rations
Two Rings: Invisibility (identified when worn) and Regeneration (heals you when you rest so you don't have to cast healing spells, tested by choosing not to cast healing spells on rest)
Two Cloaks: Protection (improves AC by 1) and a cursed one that worsens AC by 1

Food availability and consumption are both at the lowest setting, so the lack of rations isn't yet a problem.

Potions of Poison (non-magical, which is rather curious) and Neutralize Poison

Grappling Hook (is one guaranteed to be found on the first level?)

Two magical Maces (but I am just throwing Spiritual Hammers)

No scrolls at all

I decided to disable undead this time.

Second floor:

Finally found a couple scrolls (protection from cold and Cleric 'Dispel Magic')

I now have two potions of speed. Drinking one identifies both.

I am thinking of using my poison potion and one antidote potion to identify them. (I have another antidote.)

Slow Poison doesn't seem to last long enough to let you regain spells while resting.

No rations other than the two I started with, but I haven't had to sleep yet.

Found a ring of wisdom, giving me an extra 1st level spell (and 4th once I reach Cleric level 7).

Found a switch that removed a wall.

Found an illusionary wall. My character could detect that by walking by it. (Is that a Ranger ability in this game?)

Got paralyzed by the level boss. (What's the point of Remove Paralysis when you can't cast it while paralyzed anyway?)

Found a book that gives me a Ranger level if read. To get max XP from it, I am going to wait until I reach Ranger level 9 and then immediately use it.

Why would a poison have to be magical? It could be biological or chemical in nature. Poisons exist IRL as well. Having one general cure for all existing poisons would require magic, though.

That's probably a race ability. Courtesy of your half-elven nature.

My fighter/cleric/mage has fnished the 25th and final floor of his dungeon.

Here is a screenshot of the final score, the final boss (I guess I got the lich this time) and the list of vanquished foes: http://i.imgur.com/s1zt65w.jpg