After this week I will have a free night certificate from the current promotion. The certificate is good for only category 1-4 hotels but I am planning on staying in a category 5 hotel in July. I don't have any other personal hotel stays planned for the rest of the year so I would like to use the certificate for that stay. Is there any way that Marriott would let me use the certificate plus some points for a free night? A category 4 hotel is 20,000 points for a free night and a category 5 is 25,000 so I don't see why I couldn't get that to happen (at least mathematically).

Nope, they won't let you use the cert for anything but a Cat 1 - 4 hotel. I've had to let two of those expire because I couldn't use them and they won't let you use them for a family member either. It is only good for you. Thus, I try not to get free night certs. I only get points or miles.

I have absolutely been able to use for a family member.

+1
as long as you list the family member on the reservation it's never been a problem

OK. So basically if I only have 45k points before the trip, there is no way to pay for two nights with rewards plus the certificate. Great.

Try calling MR and see if they can convert it into points. Some have succeeded this way.

Can't hurt to call and give it a try.

Isn't a category 5 property 25,000 per night?

I've been able to have them convert the certificate to points for Mr. Kipper's account.
I just was able to do this for a cert that expires at the end of May that was on Mr. Kipper's account. I explained to the the CSR that we just would not be able to use it by then, and asked if they could extend the due date. She said they wouldn't be able to extend the due date, but instead, could cancel the certificate and give Mr. Kipper 20,000 points instead.

+1 I had same experience with the conversation and received 20k pts ^

I have been told that travel packages can be upgraded by adding points. Here's an example: let's say you need some airline miles for an airline award but don't yet need the hotel portion of the travel package. So you take a Cat 5 travel package with 100K airline miles, use the miles, but then "bank" the hotel portion of the travel package in your MR account. Later, however, you might realize that you want to use that banked hotel stay at a category 6 hotel. Marriott reps have told me that you can pay the difference in points between a Cat 5 and a Cat 6 travel package in order to upgrade the hotel stay to the higher category.

My question: let's say you have a Marriott Premier credit card from Chase and have an e-certificate (a 43J) for one night at a Cat 1-5 property. Has anyone tried adding points (such as the points difference between a Cat 5 and a Cat 6 stay) to upgrade the e-certificate to a Category 6? (That would be very tempting, but maybe I'm in dreamland with this idea.)

I've seen this question posed on the forums before and the answer was no (although I've never tried). From my experience, the only addition of points that can help is upgrading the room you got with the certificate.

Too bad Marriott doesn't offer Level Adjustment Vouchers as Best Western does, which can be combined with an award night cert. to get a room in a higher category!

Considering yourself lucky! I called and tales to 3 different agents but they all said NO to my request to convert free night cert to points!

Same for me. I've heard that people have had success with this, but I've been rejected every time.

Any tips from people who have has success?