Ldap Periodic Changed users sync

Hi, I’m trying to figure out how changed users synchronization with LDAP works. Particularly will it overwrite attributes of already imported users. For my use case, we add custom attributes to those that were imported from LDAP and want them to be unchanged after periodic changes sync. Custom attributes do not overlap with attributes from LDAP, they are completely different.

Will changed users sync just replace attributes list in keycloak or it will update only specific attributes either all specified in mappers or only changed ones?