In my recent experience, there does not have to be XC/XF space when a schedule change occurs. Call the international award desk and let them know what happened. They can open up space under these conditions if the 52 minutes is an illegal connection. I would imagine it is, from international to domestic, but I don't know that for sure.

My recent experience is that UA opened up space on UA flights for 4 of us routed on UA/TG HNL-KIX-BKK when TG deleted some flights (they are switching LAX-BKK to a nonstop on the new 2-class airbus) and really screwed up the schedule. The return flight KIX-HNL would have left hours before we arrived in KIX, and the layover on the outbound in KIX was terrible .. it would have been overnight. I'm not UGS, just a lowly 1k, and none of the other travelers have status, but the international award desk just made space for all 4 of us (3 in F, 1 in C) on UA flights HNL-NRT-BKK and return. That's the routing I wanted anyway, but couldn't get it originally, and this was on a *A award too with segments between BKK/HKT.

So, if the connection is illegal, I don't think you'll have any problems getting them to switch it around for you.

-David