Felix – in response to the removal of the noxious weed (privet), provided the work is covered by and within an item of approved expenditure such as “grounds maintenance” the Executive Committee can authorise the works in order to ensure the O/C’s compliance with the Law [specifically the NSW Noxious Weeds Act (1993)]even though, technically speaking, that’s a change to the common property.
With regard to the window locks, you can find the details HERE.