Sadly they're preset since it uses player skins for the textures.

you need the base pack for this one to work www.planetminecraft.com/data-pack/too-mini-blocks/

You'll need to load in all of the blocks while you're online at least once, after that the textures are saved to your Minecraft folder and the pack should theoretically work offline.

Edit: btw you can load the blocks in a creative world using the debug packs and the textures should be saved across all of your Minecraft worlds.