If you are using 6.5 or higher of IS, you should consider using pub.client.ldap:modify. The services in pub.ldap have been depricated per the documentation.
Build a service to retrieve the existing user information from the ldap. The current list of groups can be retrieved and moved into a string list. You can then add to the list and update the ldap with it.
#webMethods#Integration-Server-and-ESB#Flow-and-Java-services