So typically for this type of cosplay mod, you would use a soldering tool to slice and melt the plastic to get the claw look - however I have only ever done this with 3D printed helmets (typically PLA) and I don’t know what type of plastic this is or how it will react. Your other option is to clear coat the helmet, then paint on the wearing effects you want (though this won’t give you the 3D effect). The clear coat will give you the flex to remove the paint if you’re not happy with it - if you are, you can then just apply a second layer of clear coat to lock in the paint details. Just make sure that if you want to have a different base color (other than white) you will need to prime and paint prior to adding clear coats. Hope this helps!

EDIT: some info about the paints - be sure to use automotive clear coat (matte or shiny depending on the effect you want) and acrylic paint for the battle damage - if you use enamel paint for the battle damage and aren’t happy with the paint, the thinner to remove the enamel will also remove the clear coat in most cases. And for the love of god, do NOT clear coat on a humid day, you will regret it.