An fx-file can be the "effect" for a material.
A material can be assigned to an entity:
(toon.fx is a fx-file countaining a toon shader)
(c-script, lite-c is similar but with pointers (MATERIAL*, ...))

Code:
BMAP bmap_toonlook = <toonlook.bmp>;

MATERIAL mtl_toon = {
	skin1 = bmap_toonlook;
	effect = "toon.fx";
}

//action: fx_toon
//title: Cartoon shading
//
//desc: 
//desc: Shades the object in two steps and paints a black line around it
//
function fx_toon() {
   my.material = mtl_toon;
}