You should be able to swap out your 3 button skill for the empty hand skill that coincides with you main hand weapon. Just have the tab buttton above it like the utility skills do.
This is an example as to why this option would be nice . I’m full shadow arts and crit and and use stealth alot, the 3 button in d/d is not that spec at all. You should have more then 2 or 3 buttons to press when playing the game. I only use p/p for unload and headshot. With p/d i could have a unload like skill for dps but also have cloak and dagger with the gun for bleeding. Then both weapon swaps have more synergy within the build.
These empty hand skills are completly useless past level 5. Even though some of them are great no one really end up using them.
Players like customization and while the trait system is great, the weapon skills however can use some work.