Hello raber95,
You can try something like this:
import clr
clr.AddReference('RevitNodes')
import Revit
clr.ImportExtensions(Revit.GeometryConversion)
clr.ImportExtensions(Revit.Elements)
clr.AddReference('RevitAPI')
import Autodesk
from Autodesk.Revit.DB import *
clr.AddReference('RevitServices')
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager
doc = DocumentManager.Instance.CurrentDBDocument
#prepare input
view = UnwrapElement(IN[0])
curves = IN[1]
#Create curveloop
loop = CurveLoop()
for c in curves:
loop.Append(c.ToRevitType())
#Set cropregion in Transaction
TransactionManager.Instance.EnsureInTransaction(doc)
view.CropBoxActive = True
view.GetCropRegionShapeManager().SetCropShape(loop)
TransactionManager.Instance.TransactionTaskDone()
OUT = view