Guard armor replacers like Sons of Skyrim will replace the meshes of those original guard armors within the mods files. Meaning the guards in Falskaar will wear the new Dwemer Markarth armors Even though they're technically new armors. I wasn't a fan of seeing Markarth specific armor so far from where it belonged so I went ahead and Fixed it. This only effects the Falskaar armor and not the Markarth Guards.

I haven't tested this with any other guard armor replacers but it should work with anything that doesn't outright replace the generic Stormcloak outfit mesh.