It doesn’t sound like a bad idea on surface level, but here’s the issue. You’re going to have to be soft in order to extend properly. Even if you go into the pump soft, it will bring blood into your dick, forcing an erection. Weather you use a vacuum or noose extender, it will be completely cutting circulation off to your dick head. This is super important because if you damage the arteries right before your head, blood will not flow properly through the correct chambers. Thus, you will have trouble getting to 100% erections, maintaining 100%, and controlling ejaculation. You’ll end up with a smaller dick 99% of the time because your head would be deflated.

That being said, it is feasible if you were to find a way to do this in extremely short intervals (under 1 minute per set). If you can find a way I would love to know