you are allowed to edit it.
regarding borders, the only real hard criterion is that if the border is not game-specific, it should be cropped off, because it adds nothing and frustrates people who want to fullscreen the video. anri or yua makes it very easy to do this. the reason game-specific borders (such as mmv's) are allowed to stay is that they are "part of the game." an argument can be made that cropping a border like that would be like cropping part of a console or pc game's hud - totally unacceptable. i know it's not a perfect analogy and that's why game-specific borders are not required - just you're allowed to leave them in if you want (which a lot of people do).
regarding borders, the only real hard criterion is that if the border is not game-specific, it should be cropped off, because it adds nothing and frustrates people who want to fullscreen the video. anri or yua makes it very easy to do this. the reason game-specific borders (such as mmv's) are allowed to stay is that they are "part of the game." an argument can be made that cropping a border like that would be like cropping part of a console or pc game's hud - totally unacceptable. i know it's not a perfect analogy and that's why game-specific borders are not required - just you're allowed to leave them in if you want (which a lot of people do).