Righto. Yeah, they can be replaced. For example, some are knurled and just press in, some are a little allen grub screw that screw in, you can buy them from a fixings company. As you can also buy a small allen headed bolt that screws in. Most are a regular metric thread.
If you want to replace the press in pin type things, best thing to do is get some roll pins. If you don't know what that is, a roll pin is made from spring steel and is a little hollow tube with a split in it all the way along its length. The idea is that you make the hole very slightly smaller than the pin, then drift the pin in. As its spring steel it will compress as its drifted in and then stay put. They're a bastard to cut to length though.....
Or, you can use a length of solid bar from a model shop (2 or 3mm dia) cut down and superglue in
