check out this:
A simplified code to your request:
import clr
clr.AddReference('RevitAPI')
from Autodesk.Revit.DB import *
clr.AddReference("RevitNodes")
import Revit
clr.ImportExtensions(Revit.Elements)
clr.AddReference("RevitServices")
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager
doc = DocumentManager.Instance.CurrentDBDocument
fRegions = FilteredElementCollector(doc).OfClass(FilledRegionType).ToElements()
TransactionManager.Instance.EnsureInTransaction(doc)
for f in fRegions:
if Element.Name.__get__(f) == "Vertical":
f.Name = "Horizontal"
TransactionManager.Instance.TransactionTaskDone()
OUT = fRegions