I'll chime in and say that supporting D is a good tactic. I'm doing this now. I'm doing the leg work for mediation for a Parenting Plan, and I'm about to take lead on financial settlement. Pretty sure SteveLW raised this on my thread. PeterB, like you, my STBXW is seething anger because I'm not giving her the simple justification she desperately wants. By leading the D my way, she's also angry at not being in control, the fantasy D she envisaged is not there. It's typical for them to find anything to be upset about (I got an SMS about leaves in the pool. It's under a tree, that happens every day). Or to ask for something so they can get upset that it wasn't done, or done well.
This is all possible because I quickly realised how much happier I'll be with a D. I'm not intending to win her back. And it puts things on my terms, not hers. If you truely think you can live with D, then go for it. Show her what D looks like, and put things in motion. It's hard, I know. And you don't necessarily need to be quick. Just start the process. I'm not going to initiate the process to sell our house. She's the one complaining about being unable to live IHS. She can sell the house and move out if it's such a problem.
I don't know when the anger subsides (two months now for me), but I know it's a reflection of her, not me. In my first BD, when the anger subsided, she started to come around. But that doesn't always happen. My BD2 is different, and I'm prepared for anger for a long time.
