I applied for an OCI name change and submitted my provincial name change certificate. A few days ago, I received my application back in the mail requesting a notarized affidavit for the name change in my OCI card and Canadian passport. The letter also instructed me to mention my previous name exactly as it appears on my Indian passport in the application form.
Additionally, there's no provision in the online form to enter my new name if I mention my old name. I suppose I'll have to utilize the notes column to include my new name.
Additional Info: I got my name change certificate from Ontario & got a new Canadian passport with an updated name & driver's License, too, before applying for OCI Misc Service.
Long story short, I think you must attach an affidavit to save time and money.