[MX-5RACER]

Don't do it. The webbing will also be stretched. People do not realize that once in an accident the webbing on the seatbelt stretches to catch you and reduce the force your body sees against the belts. If you were to reuse these after getting the retractors unlocked, you could suffer further injuries if they are ever needed in an accident again. This same thing is true with racing harnesses as well.

One more note on safety equipment like Nomex balaclavas and racing suits, they are not supposed to be washed in your home washing machine. The repeated soaking in soap will cause a build-up of the dry soap particles, most of which are flammable, and reduce the materials resistance to catching fire.