I haven't tried this yet but am considering it. Since there are 16 layers in the editor maybe you could set min/max limits to each type of texture. For instance layer 2 at max 20, layer 3 min 20 max 50, layer 4 min 50 max 70 etc. I haven't worked on terrain for a while so this may not be completely accurate but that is the idea. Kind of like the real world with texture and vegetation changing at different altitudes. This would take a lot of planning but it seems that it would be possible. You may have to adjust your terrain heights manually to accommodate this method. Like I said I haven't tried this yet but will soon. Hope it works because I need the same option.