A couple of years ago, the Palmerston North City Council wanted to build a windfarm. But there was a problem: the proposed location was a reserve, where uses other than those specified (in this case, water conservation). So, the PNCC changed the purpose of the reserve to include "renewable electricity generation". Et voila!, problem solved.
(The windfarm in question was consented by a Commission, but thanks to the conditions attached seems unlikely to be built anytime soon)
Now that precedent has come home to roost, with Hutt City Council wanting to change the purpose of Naenae's Walter Mildenhall Park to include the provision of social housing. Think about that for a moment: it means that absolutely no park or reserve in the country is safe. If a local authority wants to develop them, then they can just change their purpose to something else, subdivide them, and turn them into suburban streets.
Full details of Hutt City's proposal are here. People who oppose the circumvention of the Reserves Act in this way may wish to submit on them.