For future searchers, including me, I'll answer my own question. The track category popup menu - at least the user defined part - is just a reflection of the corresponding bitmap folder (User_Pictures). Delete the bmp, and the item disappears from the menu. To load an FX preset group with the "category," the tgs file (in the DX Settings folder) needs the same name as the bmp file.

EDIT - To be clear, in the "create a category" dialog, RB is simply copying the specified bmp and the specified tgs and giving the copied files the name specified in the first edit box of the dialog.

HTH someone. -Ron