p.s.
обратная задача выполняется уже в транзакции:
import clr
clr.AddReference("RevitServices")
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager
doc = DocumentManager.Instance.CurrentDBDocument
clr.AddReference("RevitAPI")
import Autodesk
from Autodesk.Revit.DB import *
TransactionManager.Instance.EnsureInTransaction(doc)
OUT=[[WallUtils.AllowWallJoinAtEnd(i, 1), WallUtils.AllowWallJoinAtEnd(i, 0)] for i in UnwrapElement(IN[0]) ]
TransactionManager.Instance.TransactionTaskDone()