There is no such feature at the moment which would reflect changes you make to user entries via Gluu's web UI (I suppose that's what you mean) to your backend (remote) LDAP server. There is [custom scripts feature](https://gluu.org/docs/ce/3.1.6/authn-guide/customauthn/) which allow you to implement custom logic, triggered at certain events (like user authentication or Cache Refresh pull attempt). So, for example, if your backend directory provides a REST API which could be called from one of those scripts, or you can modify it via LDAP protocol, perhaps you could develop a script that serves your needs.
May be my collegues will provide better suggestion, but to the best of my knowledge that's about it.
Could you describe a use case where such feature would shine? You are also free to create a feature request [at Github](https://github.com/GluuFederation), if you wish.