Climbing onto a roof and changing garage springs are 2 things he says he'll never do. I was surprised how specific he was about it.
He knows lots of other handymen so I'm guessing he has heard lots of horror stories. Garage springs are no joke.
Other (generally older) doors have longitudinal springs. When the door is open, the spring is uncompressed, and very easy to change. Just make sure to block the door so it can't close while you're working, and install the safety wire (it goes through the spring so if they spring breaks, it doesn't hit something).
Modern doors usually don't have this kind because they take up space in the garage. The torsion kind are on top of the door and stay out of the way.
I'm willing to believe you but can't visualize this all that well. The "extension springs" in my garage door are in the space above the tracks that the door slides on. The tracks are longer than what the door itself would require, to leave room for the springs, but... is that a problem? They're on the ceiling, and some of that space would be occupied by the motor lifting the door anyway.