Cabinet Ministers, Ministers outside Cabinet, and Ministers of State 2.26 ... 2.27 Ministers outside Cabinet have full legal powers as Ministers, and may be appointed to full portfolios. They have the same role, duties, and responsibilities as Ministers inside Cabinet, and are also bound by the principle of collective responsibility. (See paragraphs 5.22 - 5.28.) They do not attend Cabinet, but, with the agreement of the Prime Minister, may attend for particular items relating to their portfolio interests. They are usually members of one or more committees, attending other committees where relevant.
And, of course, both Winston Peters and Peter Dunne have been bound by Cabinet collective responsibility during their tenure as ministers outside cabinet, subject only to the "agree to disagree" provisions that their parties have been able to negotiate in confidence and supply agreements.
Constitutional transition I've addressed the timetable for transition and operative caretaker convention in an earlier post: > LAWS179: "Election 08 - the constitutional transition"