Thank you very much guys for your clarification khomutovspace and for your reply mad! – Indeed, I misunderstood the (essential) part of your idea to avoid „scoping“ and make shared variables immutable when editing a specific context, i.e. page, … 🙌
One conceivable solution could be to display a switch next to each shared variable in the „Variables in the main theme“ section, allowing the variable to be used as a constant in all other contexts: Set as constant that cannot be changed when editing a specific page, the corresponding shared variable becomes read only in the „Variables in current template“ section … 🖖