Dear Jeremy.
Of course I am using your LookUp plugin.
I just couldn't find a solution on my own.
Up to this point, I have studied and done everything myself. But here I need a little of your support.
 
I found what it is, it's RoomTag-> TagText but I can't change it, I just get it.

 
 
Also, if you look at the parameters of the element, you can see which family is used.

 
I published this post only because I myself cannot find a solution for 2 days.
As a solution, you can also take the fact to change the text inside the stamp through the code
 
 
 
ICollection<ElementId> SelectedElements = uidoc.Selection.GetElementIds();
using (Transaction trans = new Transaction(doc, "Change selected Elements Mark"))
            {
                trans.Start();
                int i = 1000;
                foreach (ElementId id in SelectedElements)
                {
                    Element elem = doc.GetElement(id); 
                    Room roomroom = elem as Room;
                    RoomTag requiredRoomTag = null;
                    if (roomroom != null)
                    {
                        FilteredElementCollector coll = new FilteredElementCollector(doc).OfCategory(BuiltInCategory.OST_RoomTags).WhereElementIsNotElementType();
                        foreach (Element ee in coll)
                        {
                            RoomTag RT = ee as RoomTag;
                            Room r = RT.Room;
                            if (r.Name == roomroom.Name)
                            {
                                //Required roomtag
                                requiredRoomTag = RT;
                                SpatialElementTag SETag = RT;
                                    TaskDialog.Show("YES", RT.TagText);
                            }    
                        }
                    }
                }
                trans.Commit();
            }
 
 
P.S.Is it possible to change these values?
