Since I had many AViz files to process, I developed a few python scripts to process them automatically:
change_center.py: A script to translate all atoms in a file around a new center.
filter_in.py: A script to remove any atoms outside of a box around (0, 0, 0).
extract_box.py: A script that combines `change_center.py` and `filter_in.py`, with an additional option to return the file to its original coordinates after the filtering.
filter_atom.py: A script to keep only atoms of certain type(s).
counter.py: A script that returns some statistics about the AViz file (list of different atoms, range of coordinates).
Full Example: Walk-through example of how to use the python scripts
I also developed a small framework to help write these scripts in a more streamlined fashion. The scripts are available to download at this link.