I'm going to Amsterdam in August for five nights. I already reserved the five night cert for 160k points. I'm Marriott Gold

I was given an offer from another member of flyertalk.com for a five night certificate cat 8 for 140k points.

Is it worth it to cancel my certificate.. (I mean will it mess up my ability to use the lounge?) or should I take advantage of a chance to save 20,000 MRP?

The way it would work is he'd put the cert in my name and reserve the AMS Marriott for me
I'd cancel my stay and get the points back into my Rewards account
I'd transfer 140,000 MRP into his account.