Q. Dear Rabbi, If someone was severely sick and a name was added, he got B"H well, does he now have to change his kesuvah? Thank you
A. Horav Itzchok Zilberstein Shlit"a in Aleinu Leshaveach (1 p. 611) rules that a kesuvo already written in the past does not have to be changed when a name is added, other Poiskim seem to agree (Avioh Segulos p. 468, Kuntres B'rich Rachmono 36 quoting the Steipler Gaon Zt'L, et al.). Horav Refoel Alter Shmulevitz Shlit'a mentioned to me from his own experience that he was told by a Horav Yisroel Yaakov Fisher Zt"l to change his kesuvo. (Horav Fisher, was supportive of name changing and choosing the right name as a seguloh. Please note that any changes of a kesuvo, have to be done by a competent rabbinical authority)
Horav Shlomo Miller's Shlit"a is that an existing kesuvo does not have to be rewritten.
Rabbi A. Bartfeld as Revised By Horav Shlomo Miller Shlit"a