I just so happen to have a bayonet fix and unfix animation that I've never found a use for.
You can download it
here.
You'll need to use the "arf_stick_item_to_left_hand" flag in module_animations.py in order to make it work correctly.
Thing is, in the time period that L'Aigle is set in it was pretty common to always leave the bayonet on during combat, with few exceptions (skirmishers).