Earlier this week, I needed to update my reservation, which had a suite upgrade award attached. I could have just cancelled and rebooked myself, but 1) the rates had increased, and 2) the standard suites were sold out for my dates. Ever since I got access to MHC, I have been calling the concierge line (which, as mentioned earlier, should be listed in your concierge's email signature).
I wanted to add another night to my reservation without the rates changing. I could have booked a separate reservation and had the property combine them at check in, but I wanted to see if there was a way to have the suite upgrade award extended in advance or avoid having to move rooms. (You never know, maybe all the standard suites will sell out before checking in.) I just checked my phone log, and the whole call took six minutes. I was able to extend my trip by a day, and it was done without adjusting the rates on the original reservation. Since everything was under one reservation and there was availability for the extra night, there were also no issues extending the suite upgrade award.
One thing worth mentioning: a concierge I spoke with recommended calling during your concierge's listed hours. If you have to call after hours, the Globalist line is still open, but just keep in mind that the agents outside regular hours might have limited capabilities.