How to downgrade from W10 to W8, and then later go back to W10?

I'm picking up my SP4 next week, but am NOT looking forward to Win10. I have a bunch of Win8.1 licenses at home which I'm not using and will most likely downgrade to 8.1. I remember reading that a Win10 license associates itself with the computers hardware and is forever married to it. So if I downgrade to 8.1 with a completely different license can I later on re-install Win10? Preferably a clean install so I don't lose my 8.1 license. Yeah I know, I'm a license hoarder, I still have a ton of win7 and office 10 licenses sitting around "just in case" lol.