A MEL script node lets you attach a MEL script to a scene, and have the script run whenever the scene is opened (loaded from disk) or closed (when you open another scene file or start a new scene).
See Create or edit a script node for information on creating script nodes and using them to trigger events.
You can flag certain commands via the
Security Preferences so that Maya warns you (or outright denies them) when executing scripts using this method.