Distribution services like Distrokid, CDBaby, Tunecore etc will handle the mechanical license for covers. As long as you don't change the lyrics or melody, a cover will remain a cover, even if you change a genre from metal to country. The "derivative work" carveout is to protect people from changing the lyrics to e.g. something offensive and the original rights holder being unable to do anything about it.

That being said, your idea isn't original; there's already a flood of automated AI-generated cover songs being pushed onto Spotify, and they + distributors are (allegedly) starting to actively combat this.