Programmatically call OnMouseDown() of a GameObject [solved]

Not sure what you mean with that, but you can definitely use OnMouseDown to activate something when "clicked" http://docs.unity3d.com/ScriptReference/MonoBehaviour.OnMouseDown.html

If you mean you have code in your OnClick and want to call it with another method, you could do it like this:

Let's say you have this right now;

 using UnityEngine;
 using System.Collections;
 
 public class Example : MonoBehaviour {
 
     void OnMouseDown() // You want to call this right?
     {
         Debug.Log("Yay!");
     }
 }

To make it callable, you could:

 using UnityEngine;
 using System.Collections;
 
 public class Example : MonoBehaviour {
 
     void OnMouseDown() // You want to call this right?
     {
         RunCode(); // Redirect to the actual code
     }
 
     public void AccessibleMethod()
     {
         RunCode(); // You can call this whenever you want, programmatically
     }
 
     private void RunCode()
     {
         Debug.Log("Yay!");
     }
 }

Now you can call the "OnClick / OnMouseDown" Code programmatically too :)

I hope that helps, if you still have questions, feel free to ask, otherwise please accept this answer ;)