I have not yet entered the ISBN info, and I have the ISBN ready to go, but the field will simply not allow me to add information. Am I going to have to come here now every time I want to add an ISBN? I've never had this issue before
You should have entered it when you created the book record. Now GR has assigned it an ASIN and it cannot be edited. You can contact support to have them put it in, or create a new record with the ISBN and then ask for a merge.
When did this change? It never used to do that? Having a number of entries for the same book just because Goodreads auto entered an ASIN seems not only illogical, but against the entire point?
978-1-0693421-4-0 paperback edition