daruis has made it possible to body swap with out a cage trap (http://www.bay12forums.com/smf/index.php?topic=69682.0)
oh I done this on 31.10 yet I think one can do this with 40d with dwarf companion.
this is another pointless quirk you can achieve in adventure mode but unlike the other ones I made this can be done with out need to be in fort mode(no wait you need fort mode for the cage traps but that's all).
you need to do three things for this to work
a loaded cage trap
a runesmith
and the adventure traps to be on(in the init folder).
After you created your cagetraps in a area where you won't forget where they are(pave a road to them.)
you need to get taught in one*
then go in runesmith find your adventurer's flag tab and remove the "Caged" section and click the floppy disk to save.
now during the freedom of the cage walk at least a good two embark tiles away from the cage( or keep walking until you suddenly die)
**once you kick the bucket the game will randomly(well the person who the top of the list in runesmith from a guess) select 1 creature from the area.
This is your first leap now the game will swap your character for every time you travel with any thing in the area.
Anathema found another way to do this with out cage traps and utilities and also dump a save file on the character
(http://www.bay12forums.com/smf/index.php?topic=75246.0)
now I only found two ways of staying with the same character. first one is simply walking to your destination(which is just as easy as it sounds) second and risky the Travel shuffle, where you have to Travel back you the town(area) you lost your old body to reappear in it then travel to your next destination( risky as this can lead to an ambush and either having to Travel back to the same spot or losing your character in the woods.)
if you wish to return to your old body just go back to the original spot(you might have to travel back to swap bodies.)
*best to Save before you get trap or you might corrupt the save if you screw around before jumping in the cage
** now on the issue of death ending the game by starvation or Escape means losing the ability to play as your original adventurer, so far this is pretty new so I don't know if returning and retiring will end the quantum traveling. yes it does stop the body swapping
so now with this you can finally get into the shoes of a law giver, a prisoner, a king, and many more!
edit: thanks for the alt title Kobold
edit: thanks for the alt way of doing it Anathema