Hey there. Yes, my spouse seems to have returned to baseline.
Good to hear

We've been able to have a few pretty lucid conversations that brought them back to life.
Just so I understand the timeline, was your spouse mostly back at baseline
before the conversations?
It's so confusing how I can be considered the most evil abusive person alive, then my spouse is happily putting together a fish tank about an hour later. The swings are big.
The picture I'm getting about you two (and each BPD relationship is different) is that your spouse is mostly able to get back to baseline
solo, even after a big dysregulation, and that can happen in a "relatively short" (hours, vs days/weeks) time frame. Is that accurate?
I wonder if that gives you any confidence in your choice to decline to stay in the same space listening to horrible things about yourself (or trying to placate/plead/beg/reason), and instead to exit the situation and go elsewhere/do something else for a short time.
Knowing that your spouse calls you evil/abusive during dysregulations, yet is fairly lucid once back at baseline, it may be that the "least bad" structure for your relationship involves you not being present during the dysregulations/negative times, and returning to be together when things are more stable. It sounds like the timeline could be workable (hours, whereas if your spouse remained dysregulated or not at baseline for weeks, this might be a different problemsolving discussion). It might protect you from hearing those things, protect your spouse from hurting you with those words, and protect your relationship from that kind of damage (whether "intentional" or not, hearing that you're evil damages a relationship).
Not an easy journey... the "whiplash" is a real feature and it can be confusing and difficult

...
Have you two been able to have some positive times/moments together in the last day or so?