setting pick ups to run faster, jump higher etc
what is the best way to do this using kismet? also what other player properties can be changed this way?
You wont be able to control pickups properties though kismet. You would have to create a new pickup based on an existing one.
You should probably be looking at pawn/utpawn properties, rather than player properties, and, this is indeed better to do with a custom pickup. Why? This is because, within kismet, it is often difficult to set up a kismet system to time and remove pseudo-powerups from pawns once given. Also, you may find that you are more limited with what you can do in kismet, without scripting custom kismet nodes or placeable actors, so you may as well just skip that and script the pickups, instead.