Since I skipped X1 and went from 8.5.3 straight to X2, I assume that this functionality still exists.
In 8.5.3, after a synth (Kontakt in this case) is frozen, I can double click on the name of the synth and rename it in the synth browser.
In X2, when I try to rename Kontakt in the synth browser after it's frozen, X2 just hangs.
New project, no tracks other than the frozen instance of Kontakt.
(quick fix is installed)