Tagupdatefile

[simbun]

Have you tried:
indexTag: Favorite=Blues

If you want to give it a label (otherwise it will just appear as Favorite in the control point) use:
Favorite=Blues:Favorite Blues Songs

If you follow the above you'll see what, and how a filter works. You can have many of these, but there will be some work required.

I'm still not clear whether you have, or are planning to have, other values in that tag.
The only alternative is to have it as you do now with an Indexed list, albeit there are ways to customise the values, so it would be useful if you could describe exactly how you wanted the Indexed List to look and we'll see if we can help.