What is the practice of assigning non-standard readings to personal names called?


As far as I know, there are (at least) [three types of non-standard kanji
usage](https://www.kanshudo.com/grammar/ateji) now in existence in Japan:
ateji, jukujikun, and gikun. There are also
[nanori](https://en.wikipedia.org/wiki/Nanori), the readings used for personal
and geographical names

My question is: does [reading 月 as ライト](http://www.deathnotenews.com/news/why-
is-light-yagamis-name-read-as-yagami-tsuki-guest-post-by-amaryllis) in 夜神月,
for example, fall into one of these categories? Aren't nanori, for example,
also more or less fixed, as of now, in the range of their readings? Or are
nanori only limited by one's imagination and are just a convention that
remains open for additions?




Maybe a boring answer: for name reading, there are no rules and legally
speaking, they are completely arbitrary (on condition that they sound like
names). That is, as long as you use kanjis in [the list of allowed ones for
names](https://ja.wikipedia.org/wiki/%E4%BA%BA%E5%90%8D%E7%94%A8%E6%BC%A2%E5%AD%97%E4%B8%80%E8%A6%A7),
you can 'set' the reading of your own choosing. In this sense, concepts of
ateji etc. do not exactly apply to names. Most キラキラネーム's are mostly considered
as ateji, in the sense that it is made by some sort of associations: From the
link below: 男 = あだむ(Adam), 本気 = りある(real).

  * [キラキラネームはなぜ付けられる～「命名の自由」はどこまで許されるのか](https://news.yahoo.co.jp/byline/takeuchiyutaka/20190918-00143167)

>
> 日本語には、ひらがな、カタカナがあり、漢字については常用漢字表（2136字）と人名用漢字表（863字）の合計2999字であれば、自由に組み合わせて使えます。さらに、戸籍の名の欄には漢字の読み方が記載されず、出生届に「よみかた」があるだけです。しかも、その「よみかた」には制限がないため、難解な読み方や、いわゆるキラキラネームを付けることができるのです

