Back in the EM days, I did it all the time. Wico was where we bought all the "universal" switch blades and sets of assorted contact points in both gold flashed and silver/tungsten.

there is a little tutorial buried somewhere on clays site, but i can't find it.

I just use a pair of grips with a small piece of cardboard or similar to protect the contact face. Give it a good squeeze - sometimes they look to be fitted ok and then just drop out ☺

I solder them on, much easier.

Agreed. If you don't press it just right it can cause some intermittent switch problems. Solder makes a great connection.

I've tapped the back of the contact with a ball peen hammer. Have also soldered them in too. Just double check that you have 1 switch blade instead of 2 before attaching the contact. (don't ask how i know)

Clean the switch blade & the back of the contact with a q-tip & brake clean, air dry & then put a bit of flux on the blade hole. Position the contact on the blade & just solder it on.

That's also the way I did it. A vise and a ball peen hammer to set the contact for silver contacts. However, for gold flashed and tungsten contacts I soldered only. The heavy tungsten contacts used for high current flipper switches cannot take being hammered (they shatter) so solder only for those.