Declare Global Access Level functions in MS CRM Form.

Global functions in MS CRM Form.

The way CRM adds the javascript to the page, any function defined in the onload event will only have a local scope and can only be called from within the same onload event. However, if you put the function on the window object, then it should have global scope:
window.MyCustomFunction = function() { ... }

And then you should be able to call the function from an onchange event.

Ex:
// function name = MyCustomFunction
window.MyCustomFunction = function() {
    alert("My Global Level Function");
}

1. Go to MS CRM -> Customisations -> Customise Entity -> Choose Entity -> Form and View
2. Go to OnLoad()
3. Put the above fucntion onLoad() // Should be first statment.
4. Go to OnSave()
5. Call this function, MyCustomFunction();
6. When you try to save the entity record this fucntion will get executed.

Hope you enjoy this tip.