Here is the official synopsis of episode 5.12 Swap Meat.
SAM’S BODYSNATCHED! Gary (guest star Colton James), a teenage nerd, conjures up a body-switching spell and changes bodies with Sam. Thrilled by his new handsome and built body, Gary (now Sam) investigates a case with Dean and takes advantage of his good looks and age by hitting on women and getting drunk. Meanwhile, Sam is stuck in Gary’s teenage body, dealing with intrusive parents and high school. Episode written by Julie Siege with story by Julie Siege, Rebecca Dessertine and Harvey Fedor. Directed by Bob Singer.
A tiny comment: Looks like a filler episode, but I feel that this could be a light version of After School Special, with Sam (trapped in a teenager's body) going back to high school and has to deal with intrusive parents and high school. We know how Sam managed to live his high school years in After School Special, so it could be interesting to see if Sam (now Gary) deals with teenage life. Looks like it is an episode for Jared Padalecki to show us his acting chop. Another reason to like this episode already is that I like episodes written by Julie Siege and directed by Robert Singer :D