What was the process by which 有職読み applied to personal names?

Question

In premodern Japanese, it was traditional for a prestigious or extremely honorable man whose name was read with kun'yomi to have the reading of his personal name changed to on'yomi in certain situations, a process called 有職読み【ゆうそくよみ】. (Women virtually never had 有職読み, presumably because Heian period women were not supposed to read kanbun.) Some notable examples of this include:

• 源 頼光 Minamoto no Yorimitsu (944-1021), who became Minamoto no Raikô
• 徳川 慶喜 Tokugawa Yoshinobu (1837 - 1913), who became Tokugawa Keiki
• 伊藤 博文 Itô Hirobumi (1841 - 1909), who became Itô Hakubun
• 原 敬 Hara Takashi (1856 - 1921), who became Hara Kei

I have read that 有職読み applies especially after the individual's death. However, Wikipedia doesn't bear this out and it also has some odd counterexamples:

• 野沢 那智 Nozawa Nachi (1938 – 2010) was asked whether his personal name's real reading was Yasutomo and said that he wasn't sure.
• 横溝 正史 Yokomoto Seishi (1902 – 1981) had a kun'yomi on his birth certificate but it was never used.

So, two questions I'd like to have verified: is there a general rule by which the use of on'yomi is applied, and has it ever applied to people born after 1945? Is it entirely arbitrary, or was there a rule that was abandoned at some point?

Answer 1

As the comments helpfully indicated, what I've written above is actually an academic myth, based on misreading of a book published in 1980.

「読み癖」と同義だったはずの「有職読み」は、角田文衛『日本の女性名』が誤読され、そこにウィキペディアが介在したことにより、 「名の字音読み」の意で用いられ始めた。定着から僅か十年程度の幽霊語である。名乗訓みの方が「有職読み」の条件を満たしていること、近代の人名音読は「ゐなかよみ」の性質を多分に有していることなどから、この語を用いるべきではないと考える。

有職読み [meaning something like "formal reading"], which should rather be synonymous with "common parlance" [i.e. a common reading of a name or word], has started to be used in a way meaning "on'yomi personal name" as a result of a misunderstanding of the book Japanese Women's Names by Bun'ei Tsunoda which was imported into Wikipedia. This is a ghost word which has begun to appear in the past 10 years [i.e. as Wikipedia has become more widely cited]. Now, kun'yomi name reading is rather the more "formal reading" [because it follows rigid rules], while the pronunciation of personal names in the 1868-1945 period was often a "rustic reading" [i.e. based on sight and acquaintance, and freely variant], so we are of the opinion that the term 有職読み should not be used.

And to add another note, 有職読み probably became a "ghost word" because the way it is constructed sounds like it is a formal, theoretical term, whereas in fact it was simply a product of Tsunoda's writing style.

To answer my own question, there have never been formal rules determining whether to read a name through kun'yomi or on'yomi; the two used to be freely mixed, while kun'yomi became standard after 1945, until the invention of kirakira names which destroyed society forever.