Alrighty,

After a bit of reasearch, I came up with this:

http://www.radgametools.com/granny/download.html

You can freely Download the Granny Viewer, which comes with 2 sample .gr2 files, which may help you ellucidate some things if you can analyse them.

It seems like Radgametools however holds the licences (and they seem a greedy bunch too), many other games have this issue, and I got this from moding forums of AOEIII.

Correct me if I am wrong but from what I understand what your trying to do here is break the .mesh format not the gr2 format, and then if you can do that it could be reversible providing us with a way to do some modeling.

I will be looking for alternatives such as using .xml templates to probably be able to mix and match models (Body of A with head of B) from existing stock models (should not be against any licensing doing that).

I wish success to you :)