The New Zealand Electricity Regulations 1997 (5 September 2005) states in Part 3 clause 17 (2):
The following work is deemed not to be prescribed electrical work:
(a) work on— (i) electrical installations; or (ii) fittings or electrical appliances—that are intended solely for connection to, or are associated with, electricity supplies not exceeding extra-low voltage:
(b) repairs or adjustments to works, electrical installations, fittings, or electrical appliances or the replacement of extra-low voltage or mechanical fittings in electrical installations or electrical appliances, provided (in each case) that the work can be undertaken without removing any screens, covers, or the like designed to prevent inadvertent contact with fittings intended to be supplied at voltages above extra-low voltage:
Extra-low voltage means any voltage normally not exceeding 50 volts AC or 120 volts ripple-free DC.
Part 3 Clause 47 states:
Home-owners’ electrical wiring work
(1) For the purposes of section 110 of the Act, any person to whom that section applies may do or assist in doing the following work on low voltage electrical installations:
(a) remove and replace any of the following kinds of fittings, where the work does not involve work on any switchboard: (i) switches: (ii) socket outlets: (iii) permanent connection units: (iv) light fittings: (v) batten holders: (vi) cord grip lampholders: (vii) ceiling roses: (viii) flexible cords connected to any permanent connection unit, ceiling rose, or cord grip lampholder: (ix) water heater switches: (x) thermostats: (xi) elements:
(b) remove and replace fuse links:
(c) connect and disconnect fixed wired appliances:
(d) relocate existing switches, socket outlets, and lighting outlets that are supplied with electricity by toughplastic-sheathed cables:
(e) install, extend, and alter subcircuits (including submains), provided that— (i) the person must not enter (whether personally, by holding any material or equipment, or otherwise) any enclosure where live active conductors are likely to be present; and (ii) the work is tested by a registered electrical inspector, in accordance with NZS 3019, and the work is certified by that inspector in accordance with regulation
39, before being connected to a supply of electricity by such an inspector.
(2) A person who carries out work pursuant to section 110 of the Act must carry out the work in accordance with the requirements of ECP 51.
What does all this mean?
 all extra-low voltage works are not classed as electrical work.
 Home owner can remove and replace any existing 240v light fitting.
Therefore the only part of the installation that you will need a licensed Electrician for is the installation of the outdoor power-point that you will plug the transformer into if you do not already have one.