Protect Parts of my FLA

Hi Guys,

I have created a flash file and the company I have created it for now wants the fla
so they can make changes to certain parts of the action script. There are some elements that I want to protect as it took me months to develop. Can anybody give me a solution of how I can send them the FLA but at the same time protect the most important parts of my code? I was thinking that I could maybe create an external .as file for the bits of code that they want to change and like my fla to those parts. Is that possible?

If so please tell me how. Many Thanks