In your example if you are in VMC and allowed AND ABLE to operate under VFR, switch to VFR, same as any stage of flight, otherwise I would suggest you must immediately initiate a missed approach.
This is the logical way of putting it I was trying to get at.
Would that argument hold water if you had to justify your actions to the regulator?
"I conducted a full instrument approach to straight in minima then changed to VFR for the remaining 2 minutes of the flight to circumvent IFR circling requirements".
From a practical point of view I don't see much of a problem with it but somehow I don't think CASA would like it too much.