| Finoan |
I'm not aware of any feat that lets you trade some of the standard damage (or attack bonus) for crit spec effect.
And I'm not sure it would be a good trade to make either.
There are a billion ancestry feats that will give crit spec for ancestral weapons, such as Gnome Weapon Familiarity and Catfolk Weapon Familiarity.
There are some feats that do extra damage in place of a crit spec effect. Accursed Touch for example.
There are also archetype feats that give crit spec access to specific weapons or weapon groups such as Performative Weapons Training and Mauler Dedication.
So with so many ways to get crit spec, I don't think I would spend a feat to get it with an added downside of lowering base damage.