Permission for changing the title of a paper
What you write seems fine. Until very late in the process, the title should, in my view, be tentative. It should best express what the paper says. Especially if recommended revisions have changed that, or your view of it, by all means change it and just let the editor know. 

If you get pushback, or refusal, from an editor, you can deal with it then. But, IMO, it would be improper to refuse.