I think you could achieve the fun with a slightly different take.
Do a mind swap - so one character takes on the body and abilities of a different character and "encourage" them to pretend to be the character they have been swapped into.
How you do this will be different for different games. Some, like Mutants and Masterminds would be straight-up changes in power-sets and maybe physical attributes. D&D can do this with the standard polymorph rules (although that could get heavy if they have lots of stuff. In something like FATE, you'd have to work out what was body and what was mind/soul.
Once they are swapped, you put them through a situation where they have to pretend that nothing is wrong or . Examples include tense negotiations, the wedding night of one of the PCs, or the start of criminal proceedings against them.
The risks come down to what happens when the characters swap back. If any permanent changes carry over, some players may feel hurt because somebody else mutilated the character. If it is characters who are getting angry about this, there's a good story going on. If the players are getting angry then things have gotten too far.
It all comes down to trust. That's the thing you put on the line with something like this.
There is an out if things do go horribly wrong. Swap the minds of the characters into clones/doppelgangers of their bodies - so even if something permanent does happen, it doesn't have any long-term side effects. Unless the clones aren't all destroyed...