I've been meaning to complete this and make it user friendly, but I am deciding to put it out there as it is.
This script will export the .ass file compatible with Halo 2 Tool. You can now export your models directly from Blender without having to go through any other 3d software. It supports all shader syntax, instanced geometry, and UV mapping.
This script was created out of necessity, so be prepared for troubleshooting.
Big thanks to zekilk (cyboryxmen on here) for creating the original HCE exporter script for Blender! I referenced it many times while writing this! https://www.dropbox.com/s/4w97fi3z1r31vh1/blend2halo2.py?dl=0