No one knows. There is nothing formal from Marriott stating that upgrades are allowed. I have only see reports here on FT and these people were smart enough to compile a list and codes.
I personally didnt want to wait and see, so upgraded mine a few weeks ago. OC8 to NC6. Very happy I was able to do this for a mere 30K. Big difference in Cat 5 vs Cat 6 for my destination.

Scroll back, plenty of data points.

I am happy to share my limited insights with someone who appreciates it.

Much of the value in NC7 certificates is the ability to use them at any hotel booked this year. Hopefully, you will be able to use your certificate before your preferred Cat 7 hotel becomes a Cat 8 hotel. If you can't book something that works for you, you might try downgrading your certificate instead of cancelling it. Considering the delays in making NC7 certificates available, a friendly CSR might be willing to let you convert your Tier 4-5 certificate to a Cat 6 and 150K in points.

I have an old Cat 9 package attached to a hotel, but wondering if I can unattach it and use it at StR Bora? I have 7 nights booked at 60k per night at StR Bora - can I have swap my package into this? Since it's 60k points per night?

It seems like now points advance booking is available for Sheraton properties but as they changed the system, it seems like Marriott now adds extra person charge for Sheraton hotels (while it didn't in September). Is there a way to avoid the extra person charge for Marriott or Sheraton Resorts when booking with travel package?

No, your old cat nine can only book hotels up to 50k points, cat 6 or below.

I am having the opposite problem. The Sheraton I want to book used to charge extra for the 3rd person in a room. Now that they have switched to the Marriott system the room is coded for 2 people max per room so there is no surcharge -- but you cannot book 3 people in a room, max 2. Hopefully this is just teething problems and they will get it straightened out but I emailed the hotel a week ago and have not received a reply. A query through the Marriott.com contact form gave me a useless reply to call in to the standard res number and they would help me look for availability because "availability changes constantly". They totally missed the point. There is plenty of room availability -- the new system has been set up (at least at this hotel) to incorrectly set the max guests per room to 2 instead of the previous 3 in the Starwood system. And the "fun" continues.

We were able to convert a OC9 to NC6 no problem a couple weeks ago. it just took an hour.

Today I made the call I've been dreading for 3 months. I need to cancel an attached OC8, and I want to upgrade to an unattached NC6 for 30,000 points.

Spent 30-min; rep talked to his support center and then told him that the refund value was 105K and upgrade would be 60,000.

What's the best int'l call center these days for friendly, competent reps? (I'm gold status)

I've read just about every post in both this and the old cert thread. What a mess!

I've been trying for months. I can't even find anyone who has gotten them to acknowledge the existence of it yet! What the heck have they done with all the people who (should) have gotten it from the conversion process?

Struggling with a Marriott 7 Night Certificate.... I purchased it under the 'old' system at a category 7, and recently called to have this converted to a category 5 since they don't do it automatically. Unfortunately, Marriott is now telling me this is a partial package that can only be redeemed for up 7 nights up to 115,000 points. This makes no sense, and one rep even agreed, however no one could do anything about it. They repeatedly told me I needed to find a cat 5 hotel for under that amount of points, which is impossible for 7 nights.

Under activity, it shows this when the did the 'conversion': Partial Package - 7 Nights Category 5 11/04/2018, Ordered -115,000 Rewards. The email says they used QP90, which I don't see listed anywhere in this thread.

We spent almost 2 hours on the phone across 4 reps, and no one could help. When we asked for a supervisor, they just transferred us back to the waiting pool on hold. The final person transferred us to some 'lead' advisor, who put us on hold, only to eventually hang up. Does anyone have any thoughts on what to do here? Either they converted it wrong, or Marriott reps are not familiar with redeeming these converted packages....

I gather you did not do the upgrade. That is too bad. It would have worked out OK for you. The agent does not get to pick how much your old cert is worth. Once the old cert is cancelled the system returns its refund value to your account and the refund value of your OC8 cert is 135k. The agent was basically telling you the cost of a new NC6 cert was 165k (the 105k they mistakenly thought your cert was worth plus 60k) but once they cancelled the OC8 you would have gotten a 135k refund and once they ordered the new QP99 (NC6) for 165k it would have ended up costing you 30k not the 60k the agent mistakenly quoted because she quoted the wrong refund value for the OC8 (which would not matter because the system refunds the points, not her, and the system knows the correct value of the OC8).

From the wiki:
7-night packages

• NC4 QP83 = OC5 830T/P830 (refund value: 45K)
• NC4 QP87 = OC6 870T/P870 (refund value: 75K)
• NC5 QP91 = OC7 910T/P910 (refund value: 105K)
• NC5 QP95 = OC8 950T/P950 (refund value: 135K)
• NC6 QP99 = OC9 990T/P990 (refund value: 165K)

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If it were possible, the most likely answer is the difference between the liquidation value of each certificate or 60K (105k-45K).

Has anyone noticed their cert has disappeared from the Activity page? Mine used to show there above the points transactions but when I checked just now it had vanished... I've not done anything recently as I'm still waiting for Westin to be bookable for TPs.