The button in warrior setup are just previews, you need to find an inventory station after selecting your loadout via the inventory hud (Default NumPadEnter). Just change the armor, weapons, pack, nades, mines, and name to your liking and hit save, then run into an inventory and then you are set.
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You can choose a loadout, then hit numpadenter to change the loadout's weapons, pack, grenades, or even the armor.