I don't really think it did. I really think it was the final death knoll in actual punk music, opening the doors to pop punk to take over. Even so, I don't think they changed music (good or bad) for the long term. Anything Green Day did is not more important or lasting then say The Clash, The Ramones, Sex Pistols or even Joy Division. Dookie being an "important" album to the 90's (again I'd debate this - I don't think it added anything to the conversation) does not equate to Green Day being important to music.