I guess you mean the buttons and labels of your game HUD or user-interface which always should be rendered on top of the bodies and actors?
A box2d body itself doesn't have a texture/actor/image or whatever, unless you connect it... And I hope you're not connecting your labels etc with the bodies, only if you actually want the buttons to behave physically... ;)
So if you just want to always render the buttons etc on top of the whole scene just use a second Stage
(or a second SpriteBatch) that calls its draw()
method after the scene and bodies has been rendered... This way, they will always be on top of everything else and you can use a different coordinate system for scene and HUD...
Hope it helps...