To be honest, I don't think Complete My Album is smart enough to automatically change anything. You need to manually change the artwork by copying it from one of the other album files and pasting it into the single. (You might lose the unique single artwork in the process.) You will have to update all the ID tags for the single file to match however the album files are tagged. What's worse is that Apple will always "see" the single file as being the single - it won't correspond to the actual album track (in the cloud, etc.) that's available in the iTunes catalog. Someday they'll figure it out. Until then I typically don't use Complete My Album, which also doesn't consider mastering differences between versions of the same track and sometimes also mismatches files completely.