I'm trying to remember something from approximately 18 years ago that I saw on cable TV. It was an animated sci-fi story that took place on some kind of spacecraft. The only detail I really recall is that one of the characters drank a can from a vending machine and then morphed into an alien. I was very young when I saw this so I'm pretty sure it what programming made for children. That being said, I've been trying to figure this out for the past decade with no luck, so it's possible that my memory is quite off. I do recall having seen this content on multiple occasions and I don't remember it being part of a series that I watched, so maybe it was just some short that was used to fill time between shows. The most likely networks that I saw this on are Nickelodeon or Cartoon Network.
I'm pretty sure it's an episode of The Cartoon Cartoon Show: "King Crab: Space Crustacean" in which the captain's sidekick finds a vending machine in an abandoned ship with a parasite that fuses with him into an alien species.
Tv show Alienators: Evolution Continues (Known as Evolution: the Animated Series in some regions including the United Kingdom) could fit the bill.
It is animated comic sci-fi television series based on the 2001 film Evolution.
Original release dates:September 15, 2001 –June 22, 2002
More details here.
Why it might fit:
Teenage "wannabe fireman" Wayne Grey (who's been renamed Wayne Green) – A 17-year-old firefighter-in-training. Being the first human infected with alien DNA, he develops a "sympathetic mutation", causing him to mutate parallel to any Genus strains encountered.
He changes into new "alien" every episode.
Here is intro, see if it looks familiar.