Hi, you should not change permissions on that registry key, ( and you would have repair network issues if you needed to do so in the future "access denied", that's just poor advice from that site) and you don't need to. Windows ten added metered connections for ethernet as well as wifi, from version 1703 upwards, use pc settings, network & internet, click on ethernet, then on your ssid (connection) under this you can set ethernet as metered.
The registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\NetworkList\DefaultMediaCost, already exists, the value data setting is 1 for off and 2 for on.
Edit:- a network reset or fresh connection can change this setting, so it is valid, to check if yours is effected, if you are experiencing problems,
Edited by jenae, 05 April 2018 - 02:12 AM.