No I tried in Konqueror with drag and drop.
Expecting problems of ownership, I called the super mode Konqueror
So with cp (the way you stated) , I can copy the contents of my old knoppix.img to '/' while I have booted.
I suppose there are files with the same name and the question will probably made 'do you want to overide' (as I had in SU Konqueror)
I said overide, and I had an unstable system.
Not that dramatic as a reboot brought me back a stable system.

I'll try it and as I am still intesting mode (LiveCD), no real harm can be done.