All vehicles today are so tightly engineered, they need a computer to keep systems operating within tolerances.
So what you're doing is basically replacing the computer with yourself...which isn't necessarily a bad thing....
The more things that you replace, the more things that you have to manually keep an eye on.
Problem is - is that if you still have the main computer hooked up, it could work against you and put stresses against components unnecessarily.
Add in the false sense of security of an "extended warranty" that may be quietly backed up by a third party with fine print...
It just leaves too much to chance, for me anyways.
I think a lot of mods available come from trucks in the States that are made to look like they could jump 40 cars, but are really just pavement princesses. - and they look cool.
Mitch