I think your way is probably as straight forward as it gets in Ancestry member trees! :)
I just followed your instructions, and I was able to rename the source I no longer wanted to use. I called it "Duplicate Tombstone Book" so if I come across it in a citation, I will know that I need to change the citation to the other/correct source for this book.
I still think there needs to be one "Sources" page where all sources are listed, where a source can be added, edited, and/or deleted, and where all citations to each source are listed.
In the meantime, someday when I need something to do, I will look at everyone in my tree to see if I can find the citations to the "Duplicate Tombstone Book." Yea, sure….
Thank you very much for your help with this!