It’s very tricky. By design, currently, the stars and flags are neutral in meaning - they only have meaning as far as the user decides to use them - basically they just provide a way of creating two arbitrary sets of rows
I describe how I sometimes use stars and flags at Hints, Tips and Tricks - #4 by ostephens
Based on this I definitely don’t like the idea of assigning specific meaning (like “important”) to either of these existing mechanisms. I can certainly see that being able to define an arbitrary number of different sets might be useful - which I think is what is being proposed by @thadguidry in this issue Idea to add better and new Selection Labeling for Rows/Records (not only Star and Flag) · Issue #4483 · OpenRefine/OpenRefine · GitHub. However - I’d also be a bit wary of over engineering this - the advantage of the flags/stars mechanism is it’s simplicity - as soon as it becomes more complicated I feel it loses it’s current utility
An approach I might see working (which I think goes beyond simple UX improvements) would be a tagging mechanism for rows which might be used in addition to the star/flag mechanism.