Bruce:"modification". According to the GCR: "To change a component from stock"
So, to replace the various components in the pedal assembly with an aftermarket Tilton assembly is clearly not allowed.
Typical modifications I have seen on pedals are:
-Added material to stiffen the 'arm' of the clutch or brake.
-Bent arms to reposition pedals right or left.
-additional 'pedals" attached to stock components to increase the size, add grip, or offset the usable area.
-block like extensions to effectively move the usable arc backwards.
And combinations of the above.
I suppose, too, that you could redrill the mechanism to change the fulcrum point, effort, etc as well.
Now, the rule uses the term "Foot pedals" which is not in the GCR glossary. So, there could be some discussion about what that actually entails. Which means to me that the first and the second mods, along with drilling are rather grey.
Unlikely to get you protested, in the real world, but a tilton setup? yea, that SHOULD get protested pronto.
(Warts and all)