My son sells chryslers and Rams....he told me that they love to get a modded truck if it is done well because they can add $$$ to the selling price....things like aftermarket leather, tonneau covers, nice wheels, oversize or off road tires, etc. Lift kits are a no-no, as well as engine mods like programmers....buyers shy away from those.
However, as the trade comes into the dealership, they always denounce the mods (even the good ones) and generally ignore KBB or NADA pricing...they typically use ACH (actual cash value) which takes into consideration the local market and what the vehicles are going for at auction. Hence, we see the trade-in numbers below KBB listings....again, they always value your trade-in as if there were no mods and then scam you for dents, scratches, or higher mileage!!!
It's all a big game....the dealer he works for expects to make AT LEAST $4,000 over what he pays for a trade-in....amazing!!