I was just able to do this tonight via chat. I had tried about a week or so ago (definitely in January) and was denied, told they don't do that and that I should plan a staycation, as I mentioned I couldn't use it before it expired. Now today, no issue. This was for my husband's 35k night that was set to expire March 1, 2020. No idea if they have a canned response if it's too far in advance, as I know others have had luck trying earlier. I also have 1 on my account currently expiring April 1, 2020. I will probably wait until March to try to extend that one.
Using these in LA for 4 nights in August (already had 1 applied, will have 1 more coming as my biz card fee just hit) after 6 nights at
Disneyland at GCV (super excited for this score at 7 months, which took some walking). The LA property isn't changing categories (thank goodness), and I have all the individual nights booked through the UR portal on my CSR just in case. Cancelling them individually as the free nights get applied. The first night has already moved up to "peak" so it's a good thing I already had that cert applied before that happened. The others are holding at 35k for now.