  We propose a method for reconfiguring a relay node for polarization encoded
quantum key distribution (QKD) networks. The relay can be switched between
trusted and untrusted modes to adapt to different network conditions, relay
distances, and security requirements. This not only extends the distance over
which a QKD network operates but also enables point-to-multipoint (P2MP)
network topologies. The proposed architecture centralizes the expensive and
delicate single-photon detectors (SPDs) at the relay node with eased
maintenance and cooling while simplifying each user node so that it only needs
commercially available devices for low-cost qubit preparation.
