How change "Flag Status" from "Red Flag" to "Urgent"?

I have read & implemented the custom toolbar recommended in "Name your
colored quick flags". But when I group email messages by flag status, the
header line at the start of each group still says "Red Flag", "Yellow Flag",
etc. It would be nice to be able to change that text so that the group
headings are the meanings I want to assign to each flag color.

I think I might be able to do this by creating a new field, but hope not to
have to go there. If I do have to create a new field, can I create a new
field with colored flags or something similar?

Thanks,
Roscoe