You can either edit the Assault Rifle's properties directly or create a seperate. Scroll down until you find 'AssaultRifle' and select it, this will open the properties of the Assault Rifle weapon. Scroll down that list and look for the 'Weapon' tab, this will list all the weapons in the game. Now that FO4Edit has been installed and loaded successfully, click on the little + icon next to Fallout4.esm, this should expand the list of almost everything in Fallout 4.
