Is there a way to re-assign your characters' skills at some point in the game, like you could in LoG1? I've found that focusing on light armour and weapons for a fighter character (my minotaur focused on the heavies) was sort of a poor decision.

There's 2 really good sets of heavy armor, and over a half dozen really good heavy weapons, compared to 1 "decent" set of light armor, and 3 or so "meh" light weapons. I think the devs seem to have left the light-side a bit lacking.

I was okay through most of the game with this setup, but I'm at the true-boss ending now, and I'm having a lot of trouble.

Really? Hm. Guess it's been a while since I played it, because I was almost sure that there was some magic altar or something about half-way through that let you respec once with some minor penalty.

I must be confusing that option with another game, then.

Managed to beat the end boss using a trick someone in another forum mentioned: Lure him into one of the side rooms that was a monster-pen before it was released on you. If you keep him in there, he can't use his main trick and you can just beat him to death.

Sort of a let down. I was really hoping there was some clever way you could turn the tides in your favour in this battle, but anything I could think of, he was just immune to.

Also found out afterwards that you can modify your characters through the console commands.

Pity you can't re-spec.
The skill system is sooo broken in LOG (both 1 and 2).
Unless you have played it once or twice, you will highly likely screw your characters away from being efficient.

You could activate the debug made and use the console to re-spec.

Cool, I assume that could be considered an an answer. :)
Nothing bad with 'consoling' in this type of a game.
Already, after understanding that I've wasted two golden keys, while there are more golden locks then keys, I've just spawned two and try to use them wisely now. :)