Some of the accident stories I've heard about with torsion springs comes from using the wrong size winding rod or finding something around the house to use in place of a dedicated and properly sized winding rod. It slips out of the hole and
But, if you don't know how to recognize springs on their last leg, one or both could break on you when you're tensioning it and it's pretty hard to be a safe distance when you're tensioning the spring.
And then there's knowing how much tension to load into the spring and sizing the spring properly. But, if you have the right tools and properly sized springs for the door and know roughly how many turns to initially load the spring, and you're careful to fully seat the winding rods, sure, a DIYer could do it.