Ridiculously enough some L200 have dealer approved aftermarket alarms fitted which may cause the reprograming not to work! However here is the process anyway...
Locate the diagnostic connector, 16 pin connector normally under the dash near the drivers right knee.
The earth the top left pin(Pin #1), simply run some wire from here to a solid piece of bare metal under the dash.
Close all doors
Turn ignition switch to ACC position and then back to OFF 3 times within 10 seconds
Doors should lock and unlock
Press remote lock or unlock button once
Press lock or unlock button twice within 10 seconds
Doors should lock then unlock
Repeat within 1 minute for any other remotes you wish to program.
Remove earth wire.
Done
If this does not work then unfortunately you will need to visit a dealer to get it reprogrammed as you have an aftermarket alarm system fitted, but hopefully it should be ok