If you make changes to an already edited and proofed piece, is it a good idea to go to a different editor for a final/second round of edits for the fresh eyes, or is it better to stick with someone who knows the work?
It depends! How important is continuity to you? Smaller projects—essays, chapbooks, business proposals, articles, or blogs—generally don’t require large mental investments on the part of the editor. However, if you’re working on a manuscript, anthology, or series of books, you’ll likely benefit sticking with the editor who’s familiar with your content, characters, and voice. (Assuming you had a positive experience with your first-round editor, of course.) Your original editor can spend less time reading and digesting the world and more time troubleshooting revised sections. And most editors—and I include myself here—are invested in their writers’ works. They want to guide the project to publication, and they’ll work hard to get it there.
A new copy editor must start from scratch, which can be costly. You’ll be paying them to read, reread, and scrutinize the manuscript in its entirety. This can be awesome—your new editor may approach your manuscript in a wholly different way, giving you new perspective and advice to consider. They’ll probably even catch a few mistakes your original editor missed. (We’re not perfect, after all.) On the other hand, you may not want another serious line edit, especially if you’re not interested in an additional rewrite. You can give five editors the same initial paragraph and end up with five completely different (and completely okay) generated objects.
Finally, consider the scope of your changes. My discussion above applies to substantive revisions—items for which you’d normally engage a line or developmental editor. If you’re just looking for someone to correct grammar, formatting, and minor typographical errors, fresh eyes are fabulous. Let’s be real: you’re less likely to catch minor errors when you’re reading something over and over. I’m not immune to this phenomenon. When I finish editing an item at my day job (which is in a particularly litigious industry), I immediately send it to someone who’s never read it for proofing. Sometimes many people will proof it, further reducing error incidence. You can apply the same approach to your own work.
Hope that helps!