Workaround for cc reward voucher?

This is a supplementary question to my earlier on on the cc reward voucher expiry date.

I've read on some other forums people saying that you can book flights using the voucher and then move the dates back in order to get around the expiry date. I just wondered if anyone here had done this and if there were any risks if they refuse to do it (presuming that you could just cancel and pay the fee?) Thanks