mate, well done !! no one can ask better of anyone than to ask if you dont know, thats exactly what you are doing, and you have had some usefull replies. All a light is, is an electrical accessory, it is to be treated with no less than the full works of BS7671, Part P, and especially fire regs- Approved doc B, approved doc a (structures )-and any ive forgotten.
New lights come with problems, is there a CPC in the existing circuit ? bit of a minefield, You cant really do just a course on installing lights, as a minimum its off to college for you on a full course! Very well done for knowing your limitations, thats not being reckless with the publics safety. P.S. of course havent mentioned the inspect and test of new circuits,(college course ) Fluke or Megga testers ÂŁ600-ÂŁ800 each, just giving you some hints as to the lines you should be thinking along.