Clouds and sky can be manipulated in a variety of ways. You can edit CSV weather files or w2p cloud FX files or both. Some regions accept only specific sky/cloud dome meshes (w2p DrawerMesh chunks) that vanilla clouds may not use. If such is the case, then create custom DLC w2p files with vanilla game shaders (cloud channels w2mg) and Toussaint sky/cloud dome meshes specified in Toussaint w2p files. Then, create custom Toussaint CSV weather file that links to those DLC cloud w2p files.