[Flip]

I think it depends on what they class the mods as. For example it could be argued (and was often classed as) that changing just the 'silencer' was a cosmetic modification rather than a performance one.

Suspension and brakes were 'safety' items, obviously there must be limits of what is allowed or we enter a world of type approval where a change from the specified brake pads or even tyres would potentially infringe the policy.