Plus it is fraudulent - unlikely to result in criminal prosecution but perhaps a $$ claim by WN for the airfare.

If you have a CP presumably you have 100k+ points in your account (or whatever is left) the value is much higher than a few beans that you save by breaking the rules. Doesn't seem like a good risk/reward ratio.

Note you do not need ID to get through TSA (they have alternative procedures) so I'm not sure they would care at the checkpoint as long as the alternative passenger isn't showing fake ID or a fake BP. People change flights all the time post-security due to cancellations, delays, etc. Of course there are rules relating to accuracy of the manifest.