Breaking the fourth wall with a meta joke still doesn't mean that they're the same character. It would also put us in the odd position of having to tag images of Muchimaro as from AnaAru despite the image being created years before the series was first published.
In addition, Muchimaro appears in the manga tankoubons as the author's standin. At the end of each tankoubon, Muchimaro will draw herself in a short comic situation with her editor as they discuss some facets of the story in a humorous way and behave in a manner very-unlike Michinoku. At this point they are undeniably two different characters.
I think an implication is the better way forward as this means it wouldn't imply copyright being shared as stated by the tag implications wiki page.