This has been broken since it was introduced. From within the Loadouts tab of the main menu customization screen if you select a currently saved preset, make a change, and then click the Save Loadout button on the bottom it kicks you back out to the class selection screen and does not update the selected preset.
The only way to make a change to a preset is to select it, delete it, make the change, and then save it again. It's tedious.