So high compression pistons, high lift camshaft, weight reduction, widebody kits, and the crankshaft are not removable in real life? Those upgrades aren't reversible? And there would be no reason for it anyways?
Are you sure about that? I dont believe you
High compression pistons:
Aftermarket high compression pistons almost always are what’s called oversize. So for example a stock piston might be 82.5mm in diameter, the aftermarket piston is 83mm. Fitting these pistons requires a rebore of the cylinders. To remove the 83mm pistons would mean the stock 82.5mm pistons are then not compatible with the block. In real life, there would be no reason to attempt to reverse the process of fitting high compression pistons. And nobody would be crazy enough.
High lift camshaft:
Arguably you could revert to a standard profile cam. But that would almost certainly mean accompanying upgrades such as valves and lifters would be mismatched. Again, in real life you’re going to be hard pushed to find anyone that’s attempted to go back to stock camshafts because of this.
Weight Reduction:
Stage 1, and maybe Stage 2 could/should be reversible. Without booting up the game to reference PD’s description of the first stage(s) of weight reduction, it’s impossible to say for sure, but assuming it consists of things like a lightweight bucket seat and removal of interior trim, rear seats, carpet and sound deadening, yes those things could arguably be reversible. But the more extreme methods of weight reduction are permanent. Roofs are cut off, replaced with carbon or aluminium. Panels are drilled with a hole saw, and so on. Look up the ‘world’s lightest Porsche 911’ and you’ll see what I mean.
Widebody:
If a widebody is done correctly, ie in such a way that allows the track to be widened and the wheels and tyres take advantage of the extra room, original quarter panels and wheel arches are cut and removed, and the widebody kit becomes the new arches. Removing the widebody would reveal a monstrosity of a body, that would undoubtedly be unfit for roadworthiness.
Crankshaft:
Much like the cams and pistons, removal of a crank would require stripping the engine down to a certain degree, and risking running an unbalanced engine due to the deletion of balance shafts and other supporting alterations that were carried out with the installation of the racing crankshaft. Once again, you could do it, but in real life there’s no real reason to open that can of worms.