Is it possible to add a bumpmap to a terrain, and if so, how do i do it?
Officially, it's not supported using any of unity's built-in terrain features.
However, there's an undocumented and unsupported method (which could break with future releases of unity) whereby you create a new shader with the exact name of the terrain engine's shaders. Your new shader then overrides the terrain shader giving you control to use whatever replacement you want.
See this answer: