The UK CAA automatically validate any rating on the foreign licence, so for example I can fly a multi engine aeroplane which is G reg because on my FAA ticket I have the ME rating. The same is true for endorsements - As I have the FAA "Complex" and "high performance" endorsements, I can fly a high performance trubo charged aeroplane which is G reg. I once wrote to the CAA to confirm this and they did indeed confirm this. If I were you though I'd email them to get it in writing.
The only exception to the rule if the Instrument Rating. They automatically validate it but with the limitation of "outside controlled airspace" only.
However as you're flying on a CASA licence, should you want to add a rating or endorsement to that then this would need to be done by an Ozzie FI/examiner....