Do mods increase value?

I'm in Canada I can't say for US prices

I know if I crash the truck most of the parts will still be good afterwards... But if it's totaled they won't let me take them, and if it's stolen then I loose everything.

I'd rather pay insurance.

 

Insurance will value the stock exhaust, ant then the aftermarket exhaust.
The difference is what the aftermarket exhaust adds in value.
This isn't what you laid out for it ... but the vehicle already had an exhaust.
Similar for wheels, and any other take-of parts.

Same goes for trade-in value, and only if the dealer perceives it's professionally done and in a way that will get him a higher resale.

So mods ... as folks are mentioning - best to switch back to stock. Lots of buyers may feel some mods indicate a 'sporting' use of the vehicle, and possible hard driving styles.