Replace selection box for repertoire categories with checkboxes

I'm finding the need to create many categories for our repertoire and have songs belong to at least several.  It's possible to select more than one in the "Selection box" for each song, but it's kind of a pain. And it's hard to see at a glance what categories are selected if there are more than just a few categories.  Was wondering whether it would be possible to have non-exclusive checkboxes rather than the selection box.  That would be easy to see at a glance and MUCH easier to select multiples since there would be no need to hold down the CMD (or CTL) key while selecting.