Re: Have you ever asked to be demoted?
We had this issue in terms of promotion in my agency as well, where there were only two grade tracks upwards and there was pressure to become project managers and team leaders if you wanted a higher-grade position. Recently it was floated that they are seeking to expand the roles so that tech-focused employees can have more opportunities for advancement without having to track into management per se.
(I personally haven't really sought much promotion at my current level because I'm not into running teams and would rather spend my time doing more of the actual work.)
Anyway, this is actually a common dilemma in work with specialists... where one likes the work but to advance you need to manage others doing the work instead. So it shouldn't be a shock if someone prefers to keep doing the work, unless your HR department lives under a rock; it's more a matter of your corporate culture and how they view such a thing and what their resources look like. I would just sound flexible as you talk about it with them (versus drawing hard lines) until you are sure what you want to do and have a viable escape route charted in case some doors become shut to you.
I also would not refer to it as a demotion. In terms of selling it to your company, you are offering to take your enthusiasm for the tech aspect of the job and showing your willingness to focus on the things you do best and love most, to their benefit, while allowing someone perhaps with more knack for management to take on that task.
... My toast is dark and full of terrors.