James Allan writes in The Australian on the issue of codifying the Governor-General's powers:

Normally the basic rule for any governor-general is "do as you are advised to do". It's pretty simple. That's why just about anyone could do it. The only tough time comes when it's not clear who it is that is supposed to give you advice.

Allan goes on to write that codifying the reserve powers would require every possible situation to be covered, and that the ability of the courts to review the Governor-General's actions under the reserve powers would be a bad thing. Again, we only need to look at the other Commonwealth countries (and indeed New Zealand precedent) to see these two arguments are false.

For starters, as this blog previously pointed out, there are a number of Commonwealth states following the Westminster System (Trinidad and Tobago and Jamaica) where the Governor-General / President's reserve powers are codified. In neither of those two examples can it be said that codifying the head of State's has caused the sort of instability James Allan implies.

Secondly, while James Allan rails against the "unelected" Judges being able to decide important constitutional issues, this is perfectly normal for all other Executive actions outside of the reserve powers. In New Zealand we have the famous precedent of Fitzgerald v Muldoon, where an action by the Prime Minister of the day was overruled by the Court of Appeal. Judicial review is an important constitutional check, and opening the Governor-General's actions up to such review is certainly not a bad thing.