Q. If a person is born with a certain name (Hebrew) and does not like the name and tells everyone to call them by a different name and changes their name legally, does that have any Halachic binding. For example a person is called Avigal and she really dislikes that name and asks everyone to call her Avi and changes her name legally to Avi and everyone only knows her as Avi for the last 50 years, is her name Halachikally still Avigal or would it be Avi?

A. Beis Yosef and Shulchan Aruch (E.H. 119: 18) rule that a given name which has been totally forgotten and is never used for any purpose at all including a Mi Sheberach, does not have to be written in a Get or act of divorce, since it is not anymore that person’s name. Moreover, if the forgotten name is included, the Get is invalid (Get Poshut p. 112, Levush 18, Piskei Maharitz p. 314) since the current name is now the proper one.
Horav Shlomo Miller’s Shlit”a opinion is that the same applies to all other aspects of Halacha involving names.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a