Unfortunately, Tag On Placement seems to only be available for Equipment, Fixtures, and Devices. It would be neat if this functionality was eventually extended to Accessories.
Tag By Category can be assigned to a keyboard shortcut, but it won't be a single-click process as you're describing.
If you use an annotation symbol in lieu of a Tag (like a 'DSD' label embedded in the duct section), that can be added to the accessory family file directly. You won't have as much controllability over its location relative to the accessory, but that would get you closer to a one-click solution.
