Hey there, 

I have a shelley 1pm that i intend to use to control some lights.

I've read through the ECP 51 and come up with 

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 wires 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.

To fit the shelley device I would likely need to make small modifications to the existing wiring bundle that goes to the switch ie. add a wire from loop to neutral on the shelley and add wires to / from the switched input on the shelley.

Is this considered "altering a subcircuit" or can I legally do this in my own home without getting it inspected?

Apologise if this is asked and answered somewhere, my google searches didn't turn up anything 

NB. I consider myself competent to make these changes, have relevant experience and equipment.

Cheers