How to respond to an editor's post-review comments suggesting major changes I'm not willing to make?
I would suggest the following thought experiment. Take a day (or at least a couple of hours), and fully embrace the editor's suggestions. Think about why h/she made them, and think about how you would revise your paper to fully incorporate his/her suggestions, and in what aspects it would make the paper better.
Sleep on it a couple of days. Then, if you decide you prefer not to take the editor's suggestions, you will be in an excellent state of mind to write a reply.

I carefully considered suggestion X. As pointed out by the editor, this would have advantages Y and Z, and W. [It is especially helpful to not just say the same thing word-for-word, to show that you thought about the editor's suggestions carefully.]
Nevertheless, I feel that for the most part the paper is better as is, for the following reasons: ...