I remembered seeing somewhere (but can’t find now) that you can set a photoshop layer as reference only, by putting a “!” or “#” in front of the layer name (something like !layer_name), and the layer will remain as reference only, won’t export as .png or variables.
I have a layer called “iPad margin” which just help me to frame a 16:9 picture so I can quickly see how much area is cropped if I export to iPad resolution.
I don’t need to export this layer or as variable at all, it stay there just for quick reference if I need to see the difference between iPad and iPhone resolution.
Thanks.