Every so often, a random change made in an adaptation will find its way into the original comics. They're not whole new characters, they're not a certain look, they're just...stuff. These are their stories.
A character named Changeling (Kevin Sidney) first appeared in Uncanny X-Men #35 (August 1967) as a member of the villainous Factor Three; he later secretly joined the X-Men but died the same issue. In the first episode of the X-Men animated series (1992), the creators wanted to show the seriousness of the series, so they made the character an X-Men member so they could kill him off; however, in the show, he was named "Morph". This would be the name he used when he appeared in the alternate reality "Age of Apocalypse" in X-Men Alpha (January 1995).
Spider-Man's organic web spinners
Until the Spider-Man movie (2002), Spider-Man's webs had always come from a device he invented. The creators of the movie thought it wouldn't make sense for a high school student to invent such a complex device, so they gave him organic web-spinners. The storyline Spider-Man: The Other (2005) gave him organic webshooters as well (among other new powers), but they have all disappeared after the Brand New Day storyline.
Rogue's real name
The arc reactor first appeared in the film Iron Man (May 2008) as a portable power source that powered the magnet that kept a piece of shrapnel from entering Tony Stark's heart, as well as powering the Iron Man costume. It later appeared in Invincible Iron Man #3 (July 2008), though instead called a Repulsor Technology Node, as a powerful, glowing magnet implanted in Pepper Pott's chest to keep a piece of shrapnel from entering her heart. In Invincible Iron Man #8 (December 2008), Tony has to reboot his Extremis, which causes him to get an RT node as well.
J.A.R.V.I.S. (Just Another Rather Very Intelligent System)
Tony Stark's butler, Edwin Jarvis, was adapted for the Iron Man movie (2008) as an advanced AI that controlled the Stark Mansion (and the Iron Man suit later on) and was called J.A.R.V.I.S., which was explained in the movie novelization to stand for what you see in the heading. J.A.R.V.I.S. also appears, which the same acronym explanation, in Invincible Iron Man #11 (May 2009), this time based on the personality of the real Jarvis and as the controller AI of Pepper Potts's "Rescue" armor.
Mutant Response Division