Drop this file into your layers folder, set the percentages sorted alphabetically and run with node ./setRarities.js

setRarities.js

const fs = require('fs');
const path = require('path')

function validate(basePath) {
	console.log("running validation")
	
	Object.entries(percentages).forEach(([key,val]) => {
		const folderPath = path.join(basePath, key)
		
		fs.readdir(folderPath, (err, files) => {
			if(err) {
				throw new Error(err)
			}
			const pngImages = files.filter(f => path.extname(f) === '.png')
			if(val.length !== pngImages.length) {
				console.log(key, val.length, pngImages.length, pngImages)
				throw new Error("Number of files doesn't match the percentages!")
			}
		})
	})
}

const [, , ...args ] = process.argv

const basePath = args[0] ? ('./' + args[0]) : './'

console.log("Base path: ", basePath)



const percentages = {
	Background: [
		2.00,
		2.00,
		3.00,
		2.00,
		1.00,
		3.00,
		3.00,
		3.00,
		3.00,
		4.00,
		3.00,
		50.00,
		1.00,
		6.00,
		7.00,
		4.00,
		3.00,
	],
	Base: [
		8.00,
		15.00,
		12.00,
		8.00,
		4.00,
		5.00,
		7.50,
		4.00,
		4.00,
		8.00,
		8.00,
		2.00,
		8.00,
		5.00,
		1.50,
	],
	Clothes: [
		6.00,
4.00,
1.00,
1.00,
2.00,
5.00,
5.00,
2.00,
2.50,
2.00,
0.30,
1.90,
1.00,
4.00,
3.00,
2.00,
3.00,
3.00,
2.00,
4.00,
2.00,
1.00,
0.50,
2.00,
0.30,
2.00,
3.00,
1.00,
1.00,
1.00,
1.00,
2.00,
0.08,
0.92,
1.00,
2.00,
3.00,
2.00,
3.00,
1.00,
0.20,
0.80,
4.00,
3.00,
1.00,
2.50,
4.00,
	],
	Eyes: [
		0.74,
0.80,
0.99,
15.00,
6.00,
2.00,
0.70,
4.00,
4.00,
4.00,
0.80,
3.50,
2.00,
12.00,
4.00,
4.00,
4.52,
6.00,
0.95,
2.00,
1.00,
4.00,
2.00,
3.00,
2.00,
4.00,
2.00,
4.00,
	],
	Headwear: [
		2.00,
4.00,
6.00,
0.75,
5.00,
6.00,
8.00,
1.00,
5.00,
0.80,
0.95,
5.00,
4.00,
5.00,
0.50,
35.00,
4.00,
3.00,
4.00,
	],
	Mouth: [
		1.00,
4.00,
6.00,
4.00,
4.00,
8.00,
6.00,
8.00,
4.00,
5.00,
15.00,
3.00,
3.00,
12.00,
2.00,
4.00,
6.00,
3.00,
2.00,
	]
}

validate(basePath)

Object.entries(percentages).forEach(([key,val]) => {
	const folderPath = path.join(basePath, key)
	
	fs.readdir(folderPath, (err, files) => {
		if(err) {
			throw new Error(err)
		}
		  files.filter(f => path.extname(f) === '.png').forEach((file,idx) => {
			console.log("Current file name: ", file);
			
			const ext = path.extname(file)
			const nameWithoutExt = path.basename(file, '.png')
			const formattedName = nameWithoutExt.replace(/-/g, ' ')

			const newname = `${folderPath}/${formattedName}#${val[idx]}${ext}`;
			console.log("New full file name: ", newname);
			
			fs.renameSync(`${folderPath}/${file}`, newname);
		  });
	});
	
})