Updating UCC Certificate in a Production Environment

In lieu of a better answer, or any answer, I'd say it depends on BIG-IP version and platform. In the early days, a config load like this may have taken several seconds and would have interrupted every affected VIP. As of v11 and newer platforms, the interruption is likely very minimal. Nonetheless, if a user is trying to perform an SSL handshake at the exact moment that the certificate configuration is changing, they would certainly experience a hiccup, and I'm not sure there's any way around that. I'd say it's always a best practice to do this sort of configuration change during maintenance periods.