Windows 10's installation keeps your old Windows installation for thirty days after you convert. At the end of this period, your Windows license will have been converted to Windows 10, as well, so downgrading won't be possible, and a clean install of Windows 7 or 8 will not be genuine because the activation won't work.
Which applications have you had problems with, Tuaam?
The only app problem I've experienced is with GCFscape not opening. That was easy to fix, though. I right-clicked it and clicked on a new thing called Troubleshoot compatibility. It took me through a step-by-step process where it tried to figure out how to run it, and then asked me to test it and report whether it worked. I was then able to open GCFscape. I was impressed.
