I always create the trailer after I uploaded the project.
You are allowed to make changes to the game-page, including description, banner, screenshots, cover, overall-design and trailer! Not allowed (and I don't think it's possible either) is to update the game itself (sometimes fixing game breaking bugs is tolereted)
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Yeah, it took a while to create a trailer! Actually it's not really necessary, but I enjoy creating trailers :)
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That looks like a really nice game :)
The trailer is also good but could be a little shorter (faster scenes)