Scripted Models

an advanced model editing mod for Minecraft
using scripts to render vertices, particles, and visually modify the player model

Scripted Models has examples on how to use it here

Example Mod:
download the ".txt" files to ".minecraft/ScriptedModels"
then select them in the GUI by pressing "R"

Developers

Fabric

dependencies {
    modImplementation "maven.modrinth:scripted-models:0.7.2"
}
repositories {
    maven {
        name = "Modrinth"
        url = "https://api.modrinth.com/maven"
        content {
            includeGroup "maven.modrinth"
        }
    }
}

Mods using Scripted Models

Pixel's Character Models