Position of components in the editor and handle if it already exists

[joaoaugustojr]

I'm trying to do a treatment, I have some components in blocks, like sessions. I have a component called header that contains a navbar, but is there an easy way to allow just one header component in the editor? And if the user tries to drag another one, it won't be allowed? In this same component, how can I add it to the top of the tree?