it doesn't matter if you are miles or cash. Miles is form of currency just like cash. let us know how you go. unfortunately for a no-status pleb they may play hardball.

I never had downgrade offered to me so i can't say. but if on personal trip with spare time i will gladly take some cash compensation IF they also refund full fare difference. For work trip - i think contract fare specifically say 'not suitable for downgrade' on ticket condition to prevent staff cashing in and fly on inferior trips and i will fall on this to fight back.