Officers have discretion as to issuing a summons ..... personally I would write the summons for the primary offense and give a verbal warning for the seatbelt.

10-4, that was exactly what happened to me a year ago in the same county. Cop gave me a verbal for the seatbelt but wrote me for the dead inspection sticker. He understood my reason as to why I didn't have the belt on, truck rides so darn rough it's better to bounce on the seat than to be strapped down to it. Strapped in will give you a super sore back.