From release notes of VRChat 2018.1.2:

"2018.1.1 enabled a feature to convert shaders on non-friends to Standard [shaders] with Ctrl-F. This feature is not complete or ready for release, so it has been removed"

It would be great to have this feature completed and re-enabled. Enabling by toggling would be better than having to friend somebody as well, as long as Standard shaders on non-friends is default when the feature is enabled.