I'm trying to modify a joystick electronic board to use it for another
project. The joystick buttons are the kind with graphite (I think is
graphite), something like this:
http://www.weasner.com/etx/autostar/...key-detail.jpg
and I want to replace them with electric switches of this kind:
http://hotspotairsoft.com/catalog/images/ca-p220.jpg
How should I do that? Just connect the switch to the board?

Thanks,
-ioan

Yes, use a multimeter to check which two terminals on that switch are normally open then connect those across the contact grills. You may even find that one side of each grill is connected to all the others in which case you can solder one wire to that side then to same leg on each switch. The contact grills may not have a common so check before doing this.