It's obviously greyed out to prevent you messing with settings during recording (maybe to avoid losing recordings) but in case anyone wanted to bypass this I thought I'd post a workaround that I accidently stumbled across. Not sure if there's any reason why you'd want to do it though but here it is anyway.

You will notice that during recording the installation menu is greyed out. If you want to access this menu during recording you can still do so by pressing the number 4.

Cheers
Alex

You should get this added to the FAQ