This is my first homebrew attempt and I'm struggling to find a way to make this appear in my setup. I have a racial ability created as such:

Lifeblood - When you kill an enemy within 5 feet of you, you gain temporary hit points equal to one-half your level plus your Charisma modifier. You can make an attack at disadvantage to gain this benefit even if the enemy doesn't die.

Now, I also have an optional feat tied to this trait:

The Blood is Life (Feat) -

When you make an attack to gain the benefit of Lifeblood, make it at -5 to the attack roll, instead of disadvantage.
You add your Constitution modifier to the temporary HP granted from Lifeblood.
Gain advantage on Perception checks made to locate a living creature within 60 feet of you.

Is there a way that I can have the builder detect whether or not I have this feat selected and then make the various modifications? Thanks much for any advice.