The mod changes the color to red on the bat it is used on. This effect is purely cosmetic and has no effect on weapon damage.
Weapon modifications will modify an existing weapon, and any modifications previously equipped on the weapon will be destroyed, not unequipped. Loose mods cannot be crafted. For modifications unlocked through scrapping, the corresponding weapon must be scrapped in order to learn how to craft it.
Learned when scrapping object
Crafted at a weapons workbench.
A loose mod exists in the game files, but cannot be found in-game.