I would email him back & say...

"I'm glad you're excited, but here's my confirmation & since there are no details re: non-refundable deposit, I expect you to honor my original reservation & no legally you do not get to change the terms after the fact, regardless of Marriott's special events policy. If the policy was in place when I made the reservation & it showed on my confirmation I'd be in agreement w/ you, but since it wasn't I expect you to honor the reservation as it was made. If you have a problem w/ that we can either resolve it w/ Marriott HQ or the Indiana Attorney General; your choice. I expect to keep the reservation & look forward to seeing you soon, but I will not accept after the fact a change in my reservation terms & a non-refundable deposit." Love & kisses... (ok, you can drop the love & kisses part ).

Cheers.