I’m making a wall with panels, I can put black and white panel lines in the alpha channel. Is it possible to create a shader to use this single texture but have the panels specular while the panel lines unlit?
The standard Unity specular shader works that way – uses Alpha for the shininess. You can see it says Gloss(A) in the texture slot. And can test it by adding a texture using alpha for transparency (in other words, a changing alpha channel.)