Assigning a sharedMaterial to multiple renderers that change together

I searched around but no one seemed to have the problems I'm having.

First off I have a car and I want to change the paint but all the materials are instances so I decided to instead assign all the materials to a common sharedMaterial, however nothing I do seems to be working.

I tried creating a material instance and assigning it to all the renderers.

 Material newMat = currentCar.GetComponent<GameState>().notSharedMaterial;
 
         foreach (Transform child in currentCar.GetComponent<GameState>().frontBumpers.transform) { 
             child.GetComponent<Renderer>().sharedMaterial=newMat;
         }

I tried getting the sharedMaterial from the first instance and assigning it to the cars renderers

         Material newMat = currentCar.GetComponent<GameState>().notSharedMaterial;
         frontBumpers[0].GetComponent<Renderer>().sharedMaterial=newMat;
 
         foreach (Transform child in currentCar.GetComponent<GameState>().frontBumpers.transform) { 
             child.GetComponent<Renderer>().sharedMaterial=frontBumpers[0].GetComponent<Renderer>().sharedMaterial;
         }

but no matter what I do, all the paintable parts on the car are material instances instead of the original material referenced. Is there something I'm doing wrong here? I've switched out material,sharedMaterial,created new materials and nothing I'm doing is working. Any help?