I might be talking out of my league here, but I'm assuming if the OP wanted a Prado or LX470, he would've bought one. That said, you can modify the Pajero as much as your pockets can allow. Everything from suspension / body lift kits to springs / dampers to drivetrain can be done. First thing to do would be to give it a good service with a freshen up of all fluids and lubricants. I'm assuming you want it to be better off-road? Good (relatively narrow) knobbly tires will give you excellent bite on the rough stuff as compared to the road-biased wide rubber that's common these days.
Most important of all though, is to learn to drive and get comfortable with the vehicles limits. Some vehicles are better at one type of rough terrain while others are better at other types. You have to know the limitations of your own. Only then if you reach the limits of your vehicle, can you decide for yourself of the mods you need and then you can start modifying.