can u change the rear side style to an aluminium tray on a super pursuit ute? if so, are they rated at 1 tonne?

Yes but it's not the tray that dictates the rating. It's the load rating of the suspension and wheels. The lower springs and big wheels mean the rating will still be relatively low. If you change them to 1 tonne pieces it can be rated at 1 tonne but it will basically ruin the vehicle performance wise.