i think theres a lot of guessing being going on over this one, the the plastic cap under the pedal is usually to stop damage to the pedal and carpet, and to stop is sticking.
I have heard nothing of renault giving you the option to fit NOS to a clio, also, i think that if it was a type of kick down, you would have heard of it by now, and renault wouldnt go to the extent and cost of setting up two stage throttles etc and not telling anyone about it, waste of money..
i too am taking a rough guess on the following statement as well, but just to try clearing some things up, the two stage throttle you seem to be able to see, may have something to do with the Variable valve timing, so that when the timing is altered, more air may be needed, hence the reason for the bigger flap opening, either that or it is for the ECU to open to allow an increased air flow to equal out the air / fuel mixture.
Chances are, that by forcing this pedal down further than it should go, you are damaging something...