Q:
Multitool pack doesn't change for kits?
It had nothing to do with the multitool pack.
Kits used to come with their own backpack graphics dependent on each kit back in the day. Didn’t matter what other backpack you had equipped, using a kit would equip its own backpack on you as part of a visual indicator of which kit was in use. Most players didn’t like it because it covered their own choice of back item with something you couldn’t choose, they complained about it, and the devs finally agreed and changed it. Now there’s no backpack associated with kits, just a different weapon held in the characters’ hand.