Generally there’s a few things that don’t lightmap well without custom uvs. Walls, and things that have overlapping uvs (that aren’t separate islands), and things with lots of unneeded UV splits for light maps. In my guide for this model I kept the number of UV splits low, and generally in areas you don’t see, so you don’t need to mess with having a custom lightmap channel. The light fixture in this thread also did not have custom uvs in my example, i just let UE4 auto generate them.
To change the UV channel for a texture, all you have to do is plug a texture coordinate node in the material editor into your textures and set the channel. Super easy and straightforward.