How to effect a few gameobjects with the same tag through code?,How to affect multiple GameObjects with the same tag through code?

add this:

 //add this GameObject array to the top
 private GameObject[] obstacles;

 //add this when you want to ACTIVATE the effect
 obstacles = GameObject.FindGameObjectsWithTag("obstacle"); //get all obstacles
 foreach(GameObject obstacle in obstacles) //access them individually 
 {
      obstacle.GetComponent<BoxCollider>().enabled = false;
      obstacle.GetComponent<Rigidbody>().useGravity = false;
 } 

         //add this when you want to DEACTIVATE the effect
         obstacles = GameObject.FindGameObjectsWithTag("obstacle"); //get all obstacles
         foreach(GameObject obstacle in obstacles) //access them individually 
         {
              obstacle.GetComponent<BoxCollider>().enabled = true;
              obstacle.GetComponent<Rigidbody>().useGravity = true;
         }

hope this helps you bro :D