To change the gear knob is a piece of cake and there is absolutely NO need to cut the gearstick to remove the 'lift-up reverse' (for a Punto Mk2/Mk2b).
The knob is simply pulled off by pulling up vertically (you need a bit of brute strength, but it does come off).
As far as the lift-up mechanism, once you pull the knob off, the spring comes off as well. The lifting mechanism is attached to the leather gaiter (its like a plastic tube).
You have 2 options - cut the cable tie on the inside of the gaiter at the plastic collar and remove the plastic shaft or, once you have the gaiter removed, remove the plastic ridge attached at the base on the right side of the gear stick (2x T30 or 35 hex screws if I remember).
Have a look at this thread. There is a nice picture of what I'm saying almost near the end of the thread.:
http://forums.puntomk2.co.uk/showthread.php?6448-Gear-knob!&p=94869
Total time taken - 10 minutes and NO permanent damage to any component.
Personally, I favoured removing the big plastic ridge on the right side. Biggest issue I found but soon got used to it, was that I'd overshoot 5th gear.
I've since put everything back as it was originally. Just replaced my gear knob with a Momo racing knob in leather (made especially for syringe type gear sticks). Cost me almost €135, but worth every cent.