My demo-code is a bit hacky 🙂 Especially in the part where it links the editor flag to the runtimes... But I couldn't think of a better way.
And I also just realized there might be some small issue with it: If the user changes the setting through the Editor/SpineSettings.asset's inspector directly it would not account for this change until the editor reloads (either restart or domain reload I guess?). I guess this could actually could cause some headache with some hard to track issues.