Awesome
metalsmith-rename 
Metalsmith plugin to rename entries
Installation
$ npm install metalsmith-rename
Usage
import Metalsmith from "metalsmith"
import rename from "metalsmith-rename"
new Metalsmith("./")
.use(
rename([
[/\.md$/, ".html"]
])
)
.build(err => {if (err) {throw err}})
Options
This plugin takes an array. Each item must be an array of [pattern, replacement]