Satan on The Twilight Chronicles was played by different actors in his two appearances in Episodes 3 and 6. The first was a male wearing a light blue blanket. The second was a female wearing a dark blue blanket.
Parodied in The Cinema Snob's Riki-Oh! video, where the Cinema Snob and Kung Tai Ted (a character who speaks in a perpetual Hong Kong Dub) fight it out...and Ted's voice actor changes midway through the fight, because he was bought out by a new dubbing company while the two were fighting.
In The Hillywood Show's parodies of Twilight movies, the role of Jacob was originally portrayed by Joseph Lewellyn in the first one, however in the parodies of the sequels he was portrayed by Kyle Dayton.
Also in the Hillywood Show Twilight parodies, the role of Edward, which was usually portrayed by Jacob Jost, was played by Austin Clay in the Breaking Dawn parodies.
Sort of in Darwin's Soldiers. It is not uncommon for characters to be played by multiple people. The most prominent examples were Corporal Stern and Aydin; they were originally played by Noname but with his banning from the forum, they were later portrayed by Serris and LettuceBacon&Tomato.
80's Danparodied this In-Universe with Dolly being replaced by a guy (until the real Dolly showed up), then the Crabtrees being alternately played by inanimate objects.
It's also played straight, as the voice of Ma-Ti is provided by Rob Walker.
In Welcome to Night Vale, Carlos the Scientist was voiced by series co-creator Jeffrey Cranor in his first appearance ("The Phone Call"), but since December 2013 the role has been taken over by Dylan Marron. Cranor had become uncomfortable with the implications of a straight white actor playing a queer Latino character.
Actually a case of The Nth Doctor, since the change was explained In-Universe; Apparently scientists in Night Vale occasionally need to replace their vocal cords to avoid Throat Spiders
In law school a "hypothetical" is a story made up to illustrate various situations. Lawyers delight in using wacky names (like "Boyar U. Dumm" or "I.P. Daily") and material from books and movies in these stories. Here is a page on how wills are contested with a hypothetical that explains the entire problem of two Darrins.
With Sonic for Hire, Sonic and his friends appeared in many different Dorkly Bits videos before, with some weirdness between Sonic and Tails' voice actors. Sometimes, Sonic would have Tails' voice and sometimes Tails would have Sonic's voice. In one promo involving Sonic For Hire, Tails had Earthworm Jim's voice which was hilariously out of place. But now, Sonic and the gang have found their voices and in all Dorkly Bits animations after that the cast of Sonic For Hire have reprised their roles. Dr. Robotnik however has surprisingly keep his voice consistent across all animations however.
The lead actress was replaced between seasons on Super Knocked Up.
The voice actor for Leon was replaced after just episode one of The Mark Side.