Are there any mechanisms available out of the box with Visual Studio (pre-compilation, not using code) that allow changes in one .resx localization file to cascade to others? It's a manual process to add the string to multiple files. I've seen something similar done with .config files, where they're nested and at compile time the children config files overwrite the parent.
An indirect answer to my question is use a different resource editor, such as the one outlined in this answer: https://stackoverflow.com/a/25127820/719539, the ResXManager extension: https://visualstudiogallery.msdn.microsoft.com/3b64e04c-e8de-4b97-8358-06c73a97cc68
It highlights missing items, which suited my need.