can't change material, multiple materials

I have a model of a door, that uses 2 materials, one for the actual door and one for a room number. My problem is that I can’t change the material for the room numbers, which needs to be a different one for each door. For some reason I can only drag a material onto where the material for the actual door is, not where the room number is.

Does anybody have a way to do this (preferably no scripting)

It may be easier to use a decal for the door number

also check out the free Decal System it may be a bit much for your needs but could be helpful in the future. http://forum.unity3d.com/threads/141792-Decal-System