There’s not a whole lot codified, but there are some things:
- If you’re playing a different character because one of your characters is in prison, then they’re just in prison. You’ll make an Incarceration Roll for them to see how it all went and they sensibly return in whatever shape they were in once admitted to Ironhook.
- If you’re playing a different character because they got Lost from Overindulgence, then they’re just out on a bender for some time. That’s basically it. When they come back, they’re usually free of stress and harm
So when a Players wants to play a different character just “because,” I just follow the “Lost in Vice” rules. The character is just out and about doing whatever. No Downtimes, nothing- just out on a Bender. This is a good way to get a character “patched up” without needing to spend Downtime Actions, Coin, Rep, etc. on Recovery and the like
On rare occasions, there may be times where a player might “play” 2 (or more!) characters in a Session- only 1 is really allowed to be in the Score and “benefit” from payoff: 2 Free Downtime Actions, Coin, etc. It’s up to table taste if all characters played get End of Session XP, or just those predominantly used in the session. Either way, any PCs associated with the Crew, even if not seen on screen or in a Job, gets the Stash= Tier+2 every time the Crew gets enough XP to advance. They still benefit from the Crew’s overall advancement profits, IMO.
That’s how I do things/ have seen them done