I saw this topic asking how to custom facet labels in Search UI, and I figured out a way to do that, and thought I would share. p.s. you should consider not closing topics in only 28 days. In tech forums, people may come across issues months, or even years later.
Basically, I have a custom facet, and I call a function that basically looks up a pre-defined list of labels for any given value. e.g.
<span className="sui-multi-checkbox-facet__input-text">
{getFilterValueDisplay(option.value)}
</span>
and getFilterValueDisplay() is a custom function that just holds a bunch or if statements (or however you like to look up your data).