Yes, once assigned a Network license it's necessary to close Max to release it. As a safe mesaure, there is a timer in the server that release them after some unused time, but usually it's faster to close Max.
To avoid that a specific workstation take a license from the server, you can set temporary the license mode to "Stand-alone", using the "Change License Mode" tool.
I'm sorry, but we have not plans to include options to release a license manually from Max. If a workstation require to use RailClone habitually, it should has its own license (if not, use the procedure described above). It's not our policy to promote license sharing practices.