Sorry no help. I posted and deleted when I realized I was on the wrong track.
You might try putting a rectangle in the highlight with new text, so it covers up the normal state text. Have the same rectangle (often called the "button" in template menus) as part of the normal state.
Edit: Yes, that works with some potential limitations. You have to work with the color set and highlight #s to get the original button "background" to be the same color as the background when it is included in a highlight group. And the highlight text must be a different color (different highlight group from the background) so you can see it.
Is it worth the trouble?
I have not played with the greater capabilities of bluray highlights, so there may be a whole better way to go.