Can I merge multiple materials into one? I've downloaded and imported to blender 3d models of buildings as one object from open street map. Almost every wall of the buildings imported with it's own material and it will take me ages to texture them seperately. Can I merge some of the materials? The only thing I can come up with is selecting each building on edit mode and assign it each time to the same material, which is also would take me ages to do. Any better idea?
If I got what you ask, you can make material links from all objects to one: all will get last object's material assigned. 

It works like this: select all object but one, and then select that last one object too (it will be the "active" object in the selection).

Then use the menu "make links => materials" (or CTRLL and choose "materials". See this image below: