Leaving marks (savable to png) on texture

I am trying to figure out the best way to leave marks on a texture that can eventually be savedtopng.

The player gets to beat up a character, and leave various marks on the character’s “face” – anything from papercut to large black eye bruises.

You can change the texture of the enemy’s or the player’s face based on the amount of health that is left.,You can change the texture of the enemy or players face based on the amount of health that is left.