There is no requirement that Jewish converts continue to celebrate Jewish liturgical feasts once they have been baptized. Most Jewish converts I know do not. It’s not that such things are forbidden , strictly speaking; it’s just that many do not feel the need given the new context in which they are living. It’s not so much a rejection of their past as it is an embracing of their new life in Christ (cf. Galatians 3:19-29). Of course, much depends on a person’s family history and cultural heritage. In all cases, the one thing to be avoided is falling into the problem of “syncretism,” that is, creating an amalgam which is neither truly Jewish nor truly Catholic.