Or maybe small holes in the generic baggage on sides of the mules (like the camels), where you can attach (peg in hole method) weaponry or other items specific to the era of the set. These era-specific/unique parts would be on the sprue with the figures.
This way the same generic baggage mules can still be mass produced for use in each "different" set.
I feel deeply concerned by this subject or project and would like to contribute with some personal photos, my grandfather was Lieutnant in the french foreign legion before WWII, you can see him with his men (the officer on the left of the Fourth photo.
He landed in Provence in 1944 with french troops and was kill in Germany one month before the end of the war, as Captain of his battalion, received the Legion of honor medal for bravery.
Before WWII and until 1944 he was in many french colonies (Syria, etc), fought Rommel with the british.
If Strelets is doing such a set it could be SUPER !