Let's say you finished upgrading the skill tree of that Silent Kill of yours and you choose Trauma Center for her Marquee Ability. Halfway through maxing it you found out that she could do better with ICU and now you're left with no choice but to spend skillpoints to swap her Marquee Abilities and start upgrading it again. Skillpoints is one of the most important resources in the game and grinding for it takes some of your time. The option to swap Marquee abilities is good for instances like the one I mentioned above but that's just what it do, swap. The skillpoints that have been used to upgrade Trauma Center would just stay there while you grind for skillpoints to upgrade ICU. Having an option to reset Marquee abilities might be a good addition so players who made mistakes in choosing marquee abilities would not have a hard time grinding back those lost skillpoints again.