(1) If joint parental custody begins only when the child already has a name, the name of the child may be newly designated within three months after the beginning of the joint parental custody. If one parent, at the date when the joint parental custody begins, does not have their habitual residence on domestic territory, the period does not end before the end of a one-month period after their return to domestic territory. Where the child has reached the age of five, the designation is effective only if the child agrees with the designation. Section 1617 (1) and section 1617c subsection (1) sentences 2 and 3 and subsection (3) apply accordingly.
(2) Where it is finally and bindingly established that a man whose family name has become the birth name of the child is not the father of the child, the child, on its application or, if the child has not yet attained the age of five, also on application by the man, receives as birth name the name that the mother has at the date of the birth of the child. The application is made by declaration to the registry of births, deaths and marriages, which must be publicly certified. The application of the child is governed by section 1617c (1) sentences 2 and 3 accordingly.