There's two factions battling it out in space, and the "good guys" rock up on Earth to seek the author who is changing their fate with his writing. If I recall correctly, the original author might have even died, leaving their fates unwritten, so some other locals might have to finish the writing for them.
I seem to remember the title being something like Starship Blasters or Starblasters or something like that. I actually thought the novel was one of Nintendo's "Worlds of Power" series, but it doesn't appear to be so.
I read this book in the very late 80s or early 90s, and the title was definitely something "spacey."