With Gandanur you can change the version your server is running on.
Changing the version
You can change the version the server is running on using the sv_version command. Execute sv_version table to get a list of all the supported versions. You server will be displayed in the lobby of the given version, and only clients with the same version will be able to connect.
Allowing any version
You can allow any client to connect using the sv_version any command. Your server will be listed on the version it was running before you executed this command (currently a server can be listed under only one version in the lobby). All clients will be allowed to connect. Use direct IP to connect if the player cannot find the server in the lobby!
Notes
This is useful to host a server for an older version, but use the newest server executable that is protected against all known exploits.