If your interview is scheduled while you are in the divorce process, you can change to a waiver then at the interview. However, your problem is that they might approved your I-751 without an interview....thinking you are still in marital union. That could be a real problem when you attempt to naturalize.
This is a tricky situation since there is no "separated" waiver. In the eyes of USCIS, it seems you are either married or divorced....no in between.