I run a daily scan that automatically replaces pixiv samples, so there's usually no need to request their replacement here unless it's also an MD5 mismatch.
If you have an image that is better than a post that is already legitimate (sourced from the artist's Twitter, Pixiv, Tumblr, etc...), just upload it separately and make it the parent.
List the post, the full size URL (or a /media_assets link), and (if different) the final source for each proposed replacement, like so:
post #1994224 was deleted and re-uploaded to the artist's pixiv. The bookmarklet says the similarity between that post and the version on their pixiv is 99.3%
post #1994224 was deleted and re-uploaded to the artist's pixiv. The bookmarklet says the similarity between that post and the version on their pixiv is 99.3%
I don't see a point in making a replacement, and replacements do not work for id:<=2800000 anyway (issue #4260).