John Tulla Correct
I think JT hit it on the head. I don't know which paticular airframe you are talking about but it is more than likely that if your aircraft weighs over 5700KG then it will have been certified in the Commuter or Transport category. This brings with it a whole different set of rules as far as construction, (airframe redundency), and most importantly runway performance requirements. As someone else alluded to it would mean a complete re write of the POH /AFM. Something I am sure you do not want to consider.
Now asking CASA to look at that situation in this legally rampant society ain't gunna happen.
Torres, I beg to differ with you in that an aircraft over 5700 KG can be maintained to "class B" standard under a number of circumstances but obviously you are correct if you refer to RPT.