That's how I used to mod. Confidence high, plow away! I had coded for many a years by then, so I hardly ever ran into bugs. Still, KISSing the code is important. Anytime I tried to do something that was new or rare territory for me, I KISSed it, one step at a time. Any bug I encountered was luckily in the start, rather than a random game.dat bug mid-game.
However, when you do encounter a bug mid-game, try to find the source. The best tip I can give is to play alone (no AI) as a faction (take the one you suspect first). Mod in 30x faster buildspeed and have a ton of money to speed up the process, along with 30x faster experience gain (so heroes level up to rank 10 by killing two goblins). Then build one thing at a time. First a hero, then another, then another. Try attacking creep on the map, with one at a time. Use all abilities. Pay attention. Does the game crash when your hero is hit? If that's the case, something's wrong with the armor code. Any so on, you get the idea. Try units too on this method, along with special powers.
You can also speed up the progress by using the AI, but having all of you be the same faction. It does increase the chance to find the faulty faction, but it's harder to know why it crashed. So you might try to use AI first, then remove it and play alone when you figure out which faction has the fault.
