Override common ACEs of object

pluginProto.onCreate = function ()
{
    // Override the 'set width' action
    pluginProto.acts.SetWidth = function (w)
    {
        if (this.width !== w)
        {
            this.width = w;
            this.text_changed = true;    // also recalculate text wrapping
            this.set_bbox_changed();
        }
    };

See the official text plugin.
The common ACEs could be found in commonace.js

Create instance

instanceProto.CreateInst = function (objtype,x,y,_layer)
{
    var layer = (typeof _layer == "number")?
                this.runtime.getLayerByNumber(_layer):
                (typeof _layer == "string")?
                this.runtime.getLayerByName(_layer):
                _layer;
 
    // call system action: Create instance
    cr.system_object.prototype.acts.CreateObject.call(
        this.runtime.system,
        objtype,
        layer,
        x,
        y
    );
   
    return objtype.getFirstPicked();  // return the created instance
};

Reference

Reuse system action

cr.system_object.prototype.acts.SetLayerEffectParam.call(
    this.runtime.system, // this
    param0,
    ....
);

Reuse ACE

Reuse action/condition/expression from other plugin.

Action cr.plugins_.WebStorage.prototype.acts.StoreLocal.call(webstorage_obj, key, value);


Condition
cr.plugins_.WebStorage.prototype.cnds.LocalStorageExists.call(webstorage_obj, key);



Expression 
var fake_ret = {
    value:0,
    set_any: function(value){this.value=value;},
    set_int: function(value){this.value=value;},
    set_float: function(value){this.value=value;}, 
    set_string: function(value) {this.value=value;},
};
cr.plugins_.WebStorage.prototype.exps.LocalValue.call(webstorage_obj, fake_ret, key);
return fake_ret.value


Get instance 
var plugins = this.runtime.types; 
var name, inst; 
for (name in plugins)
{
    inst = plugins[name].instances[0]; 
    if (inst instanceof cr.plugins_.WebStorage.prototype.Instance)
    {
        // get target instance 
    } 
}  

Reference - webstorage extension plugin