OK, if the separation of the figures is implemented via the hip, use method #1, but leave out the step of inverting xTran for the hip. Then use the Poser Symmetry command 'Swap Right and Left'.

If the separation is implemented via the BODY, follow the steps for Scenario #2 first, then do as above.

If the figure has none standard body parts, eg a waist, the 'Swap Right and Left' command may not work for such parts, and you may need to mirror them manually.

If you need to swap symmetry for a whole animation, ockham has a "swaptotal-allframes.py" script, but it seems to suffer the same problem of ignoring none standard body parts. It will only swap synmmetry for the individual figures, it will not help with the relitive positions of the figures.

Sorry I can't offer a more automated solution. I could probably come up with some ERC that would swap symmetry in the way you want, but it would be a bit of a clunky way to do things, the user would need to apply a pose to implement the reversed symmetry, and would need a separate pose to turn the symmetry off again. much better if you could get someone to write a py script for you.