advowson: At one time, such tools existed. I never used them, and I don't know where you would find them now. They were sometimes confusingly called "trainers", despite that they didn't train you for anything. At least some of them work poorly, if at all, under modern Windows due to their reliance on deficiencies in Windows 9x.

As far as I recall, all such tools required you to have the game open and your character loaded, and would then facilitate changing the loaded character. I don't think anyone ever bothered to figure out the save file format well enough to make a tool that could edit your character directly in the saved file.

Depending on how you want to cheat, you may be better off using DevilutionX and finding/making a modified game that does what you want, rather than trying to modify your character in the retail game engine.