I want to put a custom gear shift knob on my mk1. But i saw that it has a weird system for the gear knob, it's just pressed on, doesn't have any fittings right? So, can i put a custom one? Exist custom ones that can fit the mk1?

The original does just pull of with some force. You can put on an aftermarket one if you can use a grub screw to fasten it to the stick