How to have multiple coordinate system on part but not change main WCS

Hi,

I have Plastic part (automotive) with one WCS coordinate system and I want to work something on that plastic part (example : add rib), how do I change coordinate system on plastic part to make rib , but I don't want to change main WCS as that is coordinate system important for Car plastic part.(next process for Mold Design). IF SOMEONE CAN SEND ME YOUTUBE VIDEO or explain me what I need to have to choose in NX to have different coordinate system on part.