"just when you thought it was safe to come out..................................!"
Airservices Australia have just issued a Notam shooting down my previous argument [which was based on Euro/US data.]
They have decided that transponders should be selected to SBY prior to squawk change if you have a 'tumbler' selection unit as you may trigger someone else's code and confuse the system.
Life wasn't meant to be easy!!
G'day