code: def rewrite_references( sequence, old, new, single_ref=False ):
      
      old,new = as_id(old),as_id(new)
      to_delete = []
      for i,n in enumerate(sequence):
          if n == old:
              if new is None:
                  to_delete.append( i )
              else:
                  sequence[i] = new 
                  if single_ref:
                      new = None
          elif n == new and single_ref:
              new = None
      if to_delete:
          to_delete.reverse()
          for i in to_delete:
              del sequence[i]
      return sequence
docs: Rewrite parents to point to new in old
      
      sequence -- sequence of id references 
      old -- old id 
      new -- new id
      
      returns rewritten sequence