If it's a modern novel, you certainly won't make any money off of it (copyright law being what it is), but if you look around, you might find a nice fan fiction website where you can connect with other readers and writers who will appreciate your more satisfying conclusion.
Ulterior motive
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Regardless, this exercise will not only get you playing around with words and contemplating story structure, character development, and reader expectations, but it will give you a closer understanding of the novel in question.
So for Vonnegut's sake, start with a novel you actually like.
WARNING: TIME SUCK If you want to have some fun with rewritten (movie) endings, hop on over to HowItShouldHaveEnded.com and watch some videos. A waste time, yes, but an entertaining waste.