Let's clear some things, your level is actually a static mesh, created in 3D Editor (such as 3D Max, Blender, etc)?If yes, then, import it into editor, then apply textures for this mesh. Of course you need to assign textures in 3D Editor first!If you mean assigning textures to clean mesh in editor - then no, it's not possible.You can do it more simple - create a level with brushes in editor, then convert it into static mesh.Hope I have explained a lot.
BDX777, there're two possible ways:1. Apply textures right in "Static Meshes" window:Spoiler for Hiden: 2. Apply textures in mesh properties, through "Add" button:Spoiler for Hiden:
I had this in my bookmarks, that will help you.http://www.kf-wiki.com/wiki/Help:Creating_multi-layered_static_mesh_skins
but I can only assign one of the textures I have to the mesh