How do you apply a texture to only 1 face of a Geometry?
I separate object into objects in blender by selecting it(the object faces) & P , then in jme :
If you need to attach a particle emitter to that child also :
Node objNode = (Node)((Node)spatial.getChild("MySeparatedObj")); objNode.attach(emitter);
You can also have a UV map or 2D Texture which is painted & used for the whole object ( it’s attached to the objects downloaded from sites like sketchFab , those objects basically are large that you cannot go over each face & use a different texture with it).
usually you split into separate Geometry.
But i belive you just want own Shader where you can send texcoord2 to determine what faces will use different texture, or overlay.
Myself i just use multiple textures, and some of them are overlays so are transparent in most places.