Writing is a collaborative process. An author could defend a certain character till he or she was blue in the face, but if that character doesn't please the editor, or Paula Block at CBS Consumer Products (and Richard Arnold back when he was at Paramount's ST Office), for some reason, then the character will be tweaked.
And any character can always be killed off, or transferred, or just ignored by the next author of a series, although killing off another author's original character without discussion wouldn't be good etiquette.
Shar was created because it was realized that, after Jadzia's death, DS9 was short a regular science officer. And the Andorians had been a neglected race.
Some examples of past tweaking:
In the original manuscript of "A Flag Full of Stars", Number One of "The Cage" was a special guest watching an anniversary celebration of NASA with Robert April. By the final edited book, Robert April was sitting with an unnamed famous, but seemingly humorless, woman with long salt 'n' pepper hair. I actually
guessed it was Number One, but I was still shocked years later when Brad Ferguson told me I was correct!
Lieutenant Thralen, a Theskian with blue skin, antennae and yellow fur-like hair was an Enterprise-D crewman in the novel "TNG: Metamorphosis". His race is said to be "related" to Andorians, but "more gregarious". Jean Lorrah had intended that Thralen actually be an Andorian, but was requested by the then-Star Trek Office at Paramount to make the change, since there were "no Andorians among the Enterprise-D crew". Jean Lorrah was seemingly paying homage to some Andorian speculations from the old zine article,
A Summary of the Physiological Roots of Andorian Culture (1976) by Leslie Fish, a friend from her fanfic days (and some of those references remain, such as Thralen's "the Great Mother" deity).
Supposedly Peter David's Ensign Janos, as a talking, sentient Mugato, was originally overruled (ie. he was allowed to be white, furry, with a horn on his head, but not necessarily identified by species name, since canonical TOS never indicated that Mugatos could be sentient) but a few mentions of the term did get through at the editing stage, so when David Mack did a "New Frontier" minipedia entry, Janos got to remain a Mugato, and PAD eventually explained, in "Stone and Anvil", that Janos was a mix of several alien species, including Mugato and Caitian.
