Q. Someone that has the minhag not to learn Torah on nittel nacht, is he allowed to learn the halochos of nittel nacht written in seforim like Nitei Gavriel?
A. There is indeed in Nitei Gavriel and other seforim ample material regarding Nittel. (See also Vedorashto Vechokarto Y.D. 15, and questions 242, 960 and 1567 in this forum). On question 241 we wrote; "On the prior question, (240) it was mentioned that Nitey Gavriel (End of
the Chanukah volume) quotes eight different reasons for not learning
Torah on Nit’l Night. One of the reasons (p. 245, #2) cited in the name
of Korban Nessanel, is that it is due to mourning.
It is similar
to the prohibition on learning Torah on Tisha Beav, as Torah learning
effects happiness and those are occasions of grief, loss and
anniversaries of persecution for us. It would stand to reason, that just
like in Tisha Beav you may learn the laws that pertain to that day or
about the sad experiences, stories and happenings related to the date,
so it would during Nit”l.
Indeed the Zichronos L’ben Yerushalaim
(R’ Y . Yelin – Tome II p. 19) relates that the Zais Raanon (The Gaon of
Kutnah) would gather all his talmidim and use the occasion for exactly
that purpose."
Horav
Shlomo Miller's Shlit'a opinion is that even one who keeps this minhag, is permitted to learn the
halochos of Nittel on that night.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit'a
I'm sorry, but I was unable to locate this Korbon N'san'el. Please provide the source. If you need a reliable source from a famous Poseik about Nitel, try the letter from the Chasam Sofer in Igros Sofrim Siman 2 where he quotes his Rebbe Rav Noson Adler.. You will see there that there is no problem learning Torah on Nitel, just that there was an ancient custom to be makpid to learn at least after Chatzos. Since people have trouble learning so long, the Minhag was to sleep and get up to learn at Chatzos. There was no ancient custom to be makpid not to learn until Chatzos. Additionally, you will see there that it has nothing to do with the birth of Yoshke Pondrik per se, but with the custom of Goyim to go to the Beis Tifle at midnight. And I would think that Rav Noson Adler should be considered a big enough M'kubal to know.