Workaround for the bug with the TCP/IP settings window not working for VPNs.
1) Locate the proper rasphone.pbk file
- for a VPN defined for all users on the machine - %ProgramData%\Microsoft\Network\Connections\Pbk ("cd" there using admin cmd.exe), you must be an admin to edit it
- for a VPN defined only for current user - no need to be an admin, it is at %AppData%\Microsoft\Network\Connections\Pbk (again "cd" there by cmd.exe, since it will expand the env var in percents)
2) rasphone.pbk is where the VPNs are defined. It is an old-style INI text file.
3) The property names for the VPN definitions are mostly self-describing, but, to switch off "Use default gateway on a remote network", set IpPrioritizeRemote to 0