I know when they restrict motorbikes to a 33bhp max for license reasons they can simply do that trick on the throttle for it to comply. If only it was the same on Alfa's hey ;-)
Another one used to be washers in the exhaust ports. Just unbolt the exhaust manifold remove the offending washers, bolt the manifold back on again = an unrestricted full power bike. That was a long time ago though, so I expect things have moved on!
Anyway, back to the OP.
If your throttle is already going to 100%, allowing the pedal to go further doesn't = more than 100%. It will probably = a broken throttle potentiometer!
You can check to make sure you are getting full throttle using diags (ie AlfaDiag/MultiECUScan).
On 156 the part screwed into the carpet can work loose and reduce throttle travel slightly. Screwing it down properly gets the full travel back again.