Kakashi probably knew how to perform kage bunshin and the opening of gates.

But the idea of Kakashi copying mange is interesting. If the writer follows the examples that he's set for us in the past, then yes, Kakashi was definitely able to copy mange. But if kishimoto goes of into a tangent, giving us some B.S. reason why Kakashi couldn't copy it, then NO.

It only stands to reason that Kakashi copied it. He knew about mange's existence, but probably has never seen it with his sharingan. Now he has, therefore he has copied it.