This is a simple mod with two main features:
The first feature is a hotkey to quickly get a shield (configured by default to the vanilla shield or the Tinkers Construct battlesign) anywhere out of your inventory and put it in your off hand. That way you can get the shield into that slot quickly in case of emergency. This key is assigned to \ (backslash) by default.
The second feature is the ability to remember and restore up to three hotbar+offhand configurations. For example, if you have a goot hotbar and offhand for mining and building then you put everything you want in your hotbar and (for example) torches in your offhand. Then you press ctrl-numpad7 to remember this setup. In addition if you want to fight you prefer a shield in your offhand and a sword and bow in your hotbar. Configure that and press ctrl-numpad8 to remember that. Now you can quickly switch between these two sets by pressing numpad7 or numpad8.
You are free to use this mod in modpacks without restrictions