You need to setPosition on the draggable modifier, instead of trying to update the Modifier (Note I switched you to StateModifier)
var Engine = require("famous/core/Engine");
var Surface = require("famous/core/Surface");
var StateModifier = require("famous/modifiers/StateModifier");
var Draggable = require("famous/modifiers/Draggable");
var Transform = require("famous/core/Transform");
var Transitionable = require("famous/transitions/Transitionable");
var SnapTransition = require("famous/transitions/SnapTransition");
Transitionable.registerMethod('snap', SnapTransition);
var mainContext = Engine.createContext();
var surface = new Surface({
size: [200, 200],
content: 'drag',
properties: {
backgroundColor: 'rgba(200, 200, 200, 0.5)',
lineHeight: '200px',
textAlign: 'center',
cursor: 'pointer'
}
});
var draggable = new Draggable({
xRange: [-220, 220],
yRange: [-220, 220]
});
surface.pipe(draggable);
var mod = new StateModifier();
var trans = {
method: 'snap',
period: 300,
dampingRatio: 0.3,
velocity: 0
};
surface.on('mouseup', function() {
draggable.setPosition([0,0,0], trans);
});
mainContext.add(mod).add(draggable).add(surface);