SillyString, you are treating two different things like they were the same.
Precise Strike (Ex): At 3rd level, while she has at least 1 panache point, a swashbuckler gains the ability to strike precisely with a light or one-handed piercing melee weapon (though not a natural weapon), adding her swashbuckler level to the damage dealt. To use this deed, a swashbuckler cannot attack with a weapon in her off hand or use a shield other than a buckler. She can use this ability even with thrown light or one-handed piercing melee weapons, so long as the target is within 30 feet of her. Any creature that is immune to sneak attacks is immune to the additional damage granted by precise strike, and any item or ability that protects a creature from critical hits also protects a creature from the additional damage of a precise strike. This additional damage is precision damage, and isn't multiplied on a critical hit.
That check what weapon are you using, so your feat apply.
Slashing Grace (Combat)
You can stab your enemies with slashing weapons.
Prerequisites: Dex 13, Weapon Finesse, Weapon Focus with chosen weapon.
Benefit: When you take this feat, choose one kind of light or one-handed slashing weapon (such as the longsword). When wielding your chosen weapon one-handed, you can treat it as a one-handed piercing melee weapon for all feats and class abilities that require such a weapon (such as a swashbuckler's or a duelist's precise strike), and you can add your Dexterity modifier instead of your Strength modifier to that weapon's damage. The weapon must be one appropriate for your size. You do not gain this benefit while fighting with two weapons or using flurry of blows, or any time another hand is otherwise occupied.
That feat target a specific category of weapons, not something that you are using at that time.
It is like saying "I take weapon versatility and can use slashing grace with any kind of weapon".