Answered How to have different resources share the same TV values?

That's not the purpose of TVs. However, if you give a TV a default value when you create it, then all resources will have that value, until you change the TV value in a given resource.

You can hide the TV conditionally, for example for non-Administrator users, with Form Customization, so editor users can't modify the TV value. Or you can use a "hidden" TV type, so that it never shows, and can only be changed by editing the default value of the TV itself.

You can also use @INHERIT as the default value of a TV, then when you edit a parent resource all of its children will inherit that value.

You can use ClientConfig extra to create custom settings that can be used like any setting [[++setting_key]], and use that tag as the default value of a TV. Then if you want to change it, just change the setting value in the ClientConfig CMP - or just use the setting instead of a TV in the first place.