Here are some stories I have that deal with switching places:

Altered Identities: In this story, Marty McFly switches places wih Michael J Fox of the real world.

Time Switch: Marty '86 is trapped in 2016, while Maty Jr is trapped in 1986. The two have to pose as each other.

These are my Big Two, of course - but I other fics, which has instances of switching.

Double Trouble: In 2016, Marty and Calvin both pose as Alex - on two different occassions. Marty also poses as Marty Jr. Back in 1986, Marty Jr and Alex both pose as their respective fathers.

Kidnapped: Calvin has to pose as his twin, when he's dragged over to the Twin Pines Universe.

Like Father Like Son: Marty Sr allows his son to take his place, when he realizes just how Marty Jr wishes he could experience life as a teenager in the '80s.

Coming up:

As the second half of my NaNo project for this year, Marty Jr ends up becoming his father. The two souls will probably occupy the same body. Also, in the first half, when Marty Sr becomes his younger self of thirty years ago.

For my original fic project, Mind Warped, two characters from mutually fictional universes swap places. At least, that's what happens in the original. The sequels would bring in a fangirl from a third universe, but I haven't figured out what else happens.