> I've seen/read that I can cut these ends free and straighten it out.
It's more art than science. Like you say, one of the issues is the weight and the age of the comb. New comb is really soft and weak. Honey comb is heavy. It takes some practice to learn what you can get away with as far as straightening new, soft, heavy comb. But I would straighten it anytime I thought i could get away with it. Meanwhile, though, feeding empty bars between two straight brood combs is the best way to make sure the next comb is straight.