Have bars and boards on each window. If you give each element separate materials, we can choose which is visible. You could brick-up the bottommost windows with a separate material, also. This would give us four variations: window, boarded-window, barred-window, bricked-up-window. Broken window panes can be achieved with textures and transparency maps. No need for morphs. That new brick texture looks much better than the previous one. The repeated tiling was a little too apparent.