We propose a simple setup for the conversion of multipartite entangled
states in a quantum network with restricted access. The scheme uses
nonlocal operations to enable the preparation of states that are
inequivalent under local operations and classical communication, but
most importantly does not require full access to the states. It is based on a flexible linear optical conversion gate that uses photons, which are ideally suited for distributed quantum computation and quantum communication in extended networks. In order to show the basic working principles of the gate, we focus on converting a four-qubit entangled cluster state to other locally inequivalent four-qubit states, such as the GHZ and symmetric Dicke state. We also show how the gate can be incorporated into extended graph state network.