Probably varies by state, but in Texas it is illegal to sell or offer for sale any vehicle which the emissions system has been modified. Meaning you can’t legally sell or trade any such vehicle. Dealers will likely not take it if you ever decide to trade. And, if found out, you could be fined for selling to an individual.
The DEF system stops the emissions of nitrous oxides into the air we breath. And the diesel particulate filter system stops the emissions of unburned fuel, carbon particles, and other combustion byproducts into that same air.