Things like winamp/windows media player have a list of different file extensions that they support with a checkbox next to each one so you can choose whether it should be associated with winamp/wmp. Wmp goes a step further by showing a greyed out tick (indeterminate) if another application is associated with the file, but the user told WMP to take over it.
Something like that could work well. Perhaps with .ini files mIRC could just add an option to the right click menu because not all inis will be scripts.
