Weird behaviour of an editor extension that sets variables on other scripts.

I have an editor extension that generates unique ids for objects with selected tags, I needed to make it since unity doesn't have a reliable id system to use in a save/load funcionality. the idea is that when i'm done with making a level I run the ID dispenser and everything that needs an id has it.

The problem is for all gameobjects with a few tags it works as intended, but for a few others it doesn't - it sets the id when I run the dispenser, but then when I hit play ids are set to = "". This is an example from the editor extension:

     string prefix_pickup = "P-";
 
 void DispenseIDToPickups()
     {
         if(prefix_pickup == null || prefix_pickup == "")
         {
             return;
         }
         GameObject[] pickups = GameObject.FindGameObjectsWithTag("Pickup");
         string id = "";
         for (int i = 0; i < pickups.Length; i++)
         {
             id = prefix_pickup + i.ToString("D6");
             pickups[i].GetComponent<PickupFunctionPasser>().SetUniqueID(id);
         }
     }

PickupFunctionPasser is just a class from which all pickups inherit in my project, it has a bunch of virtual voids, so you can run override voids on those pickups through those virtual voids.

Now this is what sits on an example pickup:

 [HideInInspector]
     public string id;
 
 public override void SetUniqueID(string passed_id)
     {
         id = passed_id;
         Debug.Log("id for " + gameObject.name + " is " + id);       
     }
 
     public override string GetUniqueID()
     {
         return id;
     }

That debug.log actually returns the id that is supposed to be there, so the system works, untill i press play - then the id = ""; How do I make it stay there? And why does it stay on some other objects even though they use a setup like that?

EDIT: So I've tried using the Undo.RecordObjects and Undo.RecordObject this way:

 void DispenseIDToPickups()
     {
         if(prefix_pickup == null || prefix_pickup == "")
         {
             return;
         }
         GameObject[] pickups = GameObject.FindGameObjectsWithTag("Pickup");
         Undo.RecordObjects(pickups, "assigning ids");
         string id = "";
         for (int i = 0; i < pickups.Length; i++)
         {
             id = prefix_pickup + i.ToString("D6");
             
             pickups[i].GetComponent<PickupFunctionPasser>().SetUniqueID(id);
         }
     }

And this:

 void DispenseIDToPickups()
     {
         if(prefix_pickup == null || prefix_pickup == "")
         {
             return;
         }
         GameObject[] pickups = GameObject.FindGameObjectsWithTag("Pickup");
         string id = "";
         for (int i = 0; i < pickups.Length; i++)
         {
             id = prefix_pickup + i.ToString("D6");
             Undo.RecordObject(pickups[i], "Assigned id");
             pickups[i].GetComponent<PickupFunctionPasser>().SetUniqueID(id);
         }
     }

And the id is still set to ="" when pressing play.