^Do you have a local skateboarding association? I think you're in Berlin, right? Perhaps there's a skate e.V. or something? If there's an established way for skaters to directly communicate with city representatives, that might be a good way to get the obstacles officially relocated. If not, I'd just go the diy route and hope they don't realize/care. I wouldn't bother asking for permission as a private citizen, they most likely won't even read your inquiry in time.