Thanks for the post.
It seems from your description that recoat by itself is no longer a good measure of commissions due. Would it be easier to have your radio button set be:
recoat (no commission)
recoat (with commission)
Or to simply have another field that is either commission or "no commission" as a dropdown as you ask, or another radio button set with the same two options. In this way, you could autoenter the data into the radiobutton field as "Commission" and change it if needed.
Either way, you would have to alter the calculation on the commission field to filter out the non-commissiable options using either If() or Case() as appropriate.
Is this what you're after?