Some luggage options and additional information shown -HERE.
Instructions for similar Extension plate for KTM 690 Enduro are shown here - HERE. Installation process is same.
For Extension plate goes the same as for Luggage rack - it was designed to carry lighter soft bags and/or Rotopax container (1 gallon). It can carry as much weight as mounting points (threaded inserts in the plastic tank) can endure, but I don't recommend putting more then few kilograms to the back, because of possible bouncing issues. Checkthis blog post, to learn how to prevent bouncing of the rack.