[Fixed]-How to make a many-to-many relationship act like a foreign key relationship?

I’m afraid you cannot do it using stock Django tools. And it is for good. It prevents you from modifying the related object on another end of many-to-many, that could be in fact used by other instances.

If you feel desperate and must do it exactly like you describe, your only way is to create custom forms for your inline admin. It is described in the documentation, too.