True, but is still a legitimate edit, that does nothing to make the sprite uneditable.
You may not REMOVE another one's edits, but I've heard nothing about touching up another ones edits, as I know people have thanked others for doing such in the past.
Ok, so, the way I see it, there are 4 levels of "removal"
Removal - Where the edit is deleted, ignored, or skipped. This isn't allowed, unless said edit breaks a rule.
Replacement - Where an edit is overtaken or covered up by a subsequent edit. This could be allowed, depending on the circumstance, and amount of time between the two edits.
Modification - Where their edit is modified, and turned into something else, or things such as recoloring and/or reshading. This is allowed most of the time, depending on how much is modified.
Repair - Where the edit is poor in quality, and small touchup work is done by another in an attempt to make it look better. This is usually allowed, if the repair is actually an improvement, and doesn't make things worse.
Basically, just use common sense. If it's rule-breaking, get rid of it; if it's just bad, fix it or leave it alone; if it's in the way, you can modify it within reason.