SOLVED
hope to be helpful to someone else
Code: (without CORS)
var image = new Image();
/*image.crossOrigin = "anonymous";*/
image.onload = function () {
var texture = new pc.Texture(app.graphicsDevice);
texture.setSource(image);
var material = new pc.StandardMaterial();
material.diffuseMap = texture;
material.update();
pc.app.root.findByName("target_entity").model.meshInstances[0].material=material;
};
image.src = "external/path/for/example.jpg"; // Remember CORS