Any change *can* be made at the proof stage, but most publishers strongly discourage what we refer to as “editing in proof.” Extensive changes in proof can be expensive, and sometimes the author is charged for the additional cost. More to the point, making edits that cause text to reflow (e.g., a large insertion or deletion) can adversely affect the book’s pagination, which could have deleterious effects on the schedule and the viability of the index. When we send edited manuscripts to authors for review, we exhort them to “Make NOW all the changes you want to make, thereby obviating the need to make substantive changes after the book has been typeset.” Changes that could be allowed at the proof stage include errors of fact, typos, and egregiously bad grammar or punctuation that should have been corrected during the editing process.
Fordham University Press’s Manuscript Submission Guidelines are available here,
—Fordham University Press, May 2021
Most university presses will provide authors with specific guidelines about what can be changed in page proofs (these are the typeset pages you receive, typically in pdf form, after you’ve approved the copyedited manuscript) and what changes should be avoided at that late stage. Before your book is typeset, you will have been given feedback from your acquiring editor, peer reviewers, a copyeditor, and your project editor, so you will have had ample opportunities to fine-tune your manuscript. By the time your book goes into typesetting, it should be considered essentially final.
After a text is typeset, presses are always happy to incorporate changes that correct errors in spelling, fact, and grammar, but we strongly discourage changes that fall outside of these categories. There are three main reasons for this. First, the more we modify a typeset manuscript, despite the careful efforts of all parties involved, the more we increase the risk of inadvertent errors and inconsistencies being introduced. Second, a large number of changes could affect your publishing schedule, possibly delaying your book’s release, and changes that add significant amounts of material or move content around can affect the index if there is one. Third, changes to the proofs can be costly, because the typeset pages may need to be reflowed or, if a great number of changes are introduced, the text may need to be recopyedited and the typesetting completely redone. That is why most book contracts specify that authors can be charged for the cost of unnecessary changes to the proofs. You may also see these changes referred to as “author’s alterations” or “AAs.”
—Michigan State University Press, February 2021