Horror/bizarro author here. I have a 1st draft, roughly 65,000 words. It's a compact, but "traditional" fantasy novel. I started with the notion of "I'd like to try my hand at writing fantasy" and finished the manuscript realizing I have no right penning fantasy novels and it all feels really contrived. However, I like the core story and characters I crafted and want to salvage them, albeit in another genre. Has anyone ever overhauled a novel on a massive re-write to put it into another genre?

Is it just a matter of diving in and changing instances of the word "castle" to "space station" or "post apocalyptic outpost?" Or am I on a fool's errand?

TL;DR - I like the story I wrote but want to shift genres. It sounds daunting.