After doing this the seatbelts still work fine in "manual mode", just like in regular cars designed by nature and God's true servants.
This seatbelt bad idea thing is a robot that slides back and forth in a track up and over the door. It's a big pain in the neck. Literally and figuratively. In a horror movie it would strangle someone. When I tie things to the roof with a rope, I have to untie it from the inside before getting out or the damn slider thing runs up against it and makes breaking sounds.
The one on my passenger side was already broken on my car. That one is fine for the passengers, but the mechanism makes clicking sounds so I went looking for the source.
Step 1: What if the Seatbelt is Jammed?
Look to the right of the doorjamb. Pull off the little round cap. There's a hex socket there. Turn that with an allen wrench to manually reel the seatbelt slider to the correct position.
What if the garbage disposal unit that feeds your biogas digester is jammed?
There's a similar looking hex socket on the bottom of that. Turn it to unjam the unit.
The path to righteousness cannot be traveled in cars.
If you must get one it should be as small as possible. And don't get a new car.
That causes new production which cooks baby angels with napalm.
Your car should dine as low on the foodchain as possible.
Get a diesel to run on Waste veggie oil or biodiesel made from it, for example.
If you can't find one of those, get an old economy car in the meantime.