Sega does NOT allow editing of their work without permission:
"You acknowledge and agree that all content, design elements, and materials available on this site are protected by copyrights, trademarks, service marks, patents, trade secrets, or other proprietary rights and laws. No materials from this site may be copied, reproduced, modified, republished, uploaded, posted, transmitted or distributed in any form or for any means without Sega's prior written permission.
Furthermore, you agree to not sell, license, rent, or create derivative works from such materials or content. Systematic retrieval of content from this site to create or compile, directly or indirectly, a collection, compilation, database, or directory without written permission from Sega is strictly prohibited."

Sheezy DOES have rules on this, morons:

"Sprites: A lot of sprites have been reported as well. Edited or recolored sprites from sonic games ARE NOT ALLOWED! That is the same with the edits of Sailor moon coloring sheets. Those are not allowed either on the site." -- Radiant Hearts, Sheezy Cast

"SheezyArt does not allow stolen or “ripped” submissions on its galleries. This includes copied and pasted artwork from other sources, traced/colored artwork, music, lyrics, and/or copyrighted or trademarked characters/logos without due and proper credit."

Copyright Acts for "parodies" don't work either:
"You don't even know what a parody is to begin with. A parody mimics someone's style - and take note on the word 'mimics' - in a comical fashion. Editing, for one, is not mimicking a style, it is stealing/editing/copying it. Parodies, for two, are also DRAWN, not traced/stolen piles of smoldering shit that you think you can get away with. And third, if parodies are supposed to be funny, why do I see no humor in ANY of your work? Why doesn't it say somewhere in the description that this is a parody? And if I hadn't even come at you with this, would you even KNOW what a parody is to begin with?
Don't think you can use Copyright Acts, meant for parodies only, to back up your lazy editing shit. I fail to see why it's so fucking hard to just make a sprite from scratch."