I once attempted to enter cta with a non operational mode-c ;coming into cta for maintenance on it) for which I received a letter for. The controller warned me that it would go on record that I tried to enter cta knowingly with a non-operational mode-c. Had I said that mode-c was "not fitted" nothing would have come of it.
Receiving a letter from CASA is not that bad for an offence just as long as they don't keep appearing in your mailbox. Thinking about it though they sent my letter to me ad the operator so in theory they don't know who was driving at the time, would have to retrospectively check back to find out.