I am looking for mules to pull my artillery.

I couldn't find any in the cataloque.

With the exception of EQU03 - Pack Mules which naturally are loaded with packs.

Are there any "packless" mules?

Do you think it would be "doable" for me to attack the pack mules with knife and file, or would this do more damage to my fingers than to their packs?

I have some of these pack mules and I would say it is possible you could attack them in such a way, although personally I'd be tempted just to use the horses supplied with the limbers and call them mules ;)