I’m do not think there is a way to change the parameterization, That said, even if there were for this model, I don’t think there necessarily is for every model with latent variables that has label switching, and I found the problem pop up a handful of times on the Discourse when I was looking for a solution for my own case.
A full HMM may be overkill, but if we can think of a heuristic to sync some proportion automatically, then it might be worth it. Maybe just a warning that the automatic function will only work if there is no within-chain switching. If there is within chain switching it will probably look non-converged so you’d at least know.
But more important is some way to alter the multitrace object to correct by hand. Or to allow the diagnostics to accept arrays, but that would probably require more changes.