You can change them all except F1. And you can even change shift+F1 (and the others too) if you want. I wonder if the reason F1 can’t be changed is because it is an MS standard for F1 to invoke help. Word, Excel, Windows Media Player, etc. all use it for help, as do non-MS applications like Photoshop & Chrome. The only thing I’ve ever seen the F1 key do is invoke help for the active window if that window has a help function (and if it doesn’t, it does nothing). I’d guess that this association is occurring within the OS and not the specific application.
Even in Cubase’s Key Command window, if you hit F1 you get a help screen.