Yes, I believe you have to call set_texture() as well.
Good question. It might be possible to use a texture handle when calling go.set("#gui", “textures”, self.texture_handle, { key = “foobar” }). I suppose you have tried that already?
It says texture type is not supported:
go.set failed because the value is unsupported
Ok, well, that is perhaps something we could support in the future. Although in the long run we are merging gui and go, and then it is not a problem anymore.