A Python script for Revit, facilitating the renaming of an assembly element. It employs Revit API and Dynamo libraries, and handles transactions for renaming.

RenameRevitAssembly.py

# Rename Revit Assembly 

import clr
clr.AddReference('ProtoGeometry')
from Autodesk.DesignScript.Geometry import *

import Revit
clr.ImportExtensions(Revit.Elements) 
clr.ImportExtensions(Revit.GeometryConversion)

import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager

from System.Collections.Generic import *

import Autodesk
from Autodesk.Revit.DB import *

doc = DocumentManager.Instance.CurrentDBDocument
uiapp = DocumentManager.Instance.CurrentUIApplication  
app = uiapp.Application
uidoc = DocumentManager.Instance.CurrentUIApplication.ActiveUIDocument

assy = UnwrapElement(IN[0])
new_name = IN[1]

TransactionManager.Instance.EnsureInTransaction(doc)
assy.AssemblyTypeName = new_name
TransactionManager.Instance.TransactionTaskDone()

OUT = (new_name, assy)

To use:
insert a Transaction.End Node (to Start a new Transaction)
or use
TransactionManager.Instance.ForceCloseTransaction()

Discussion at https://forum.dynamobim.com/t/rename-newly-created-assembly/62715

This script renames a Revit assembly element to a new given name.

It imports necessary RevitAPI and Dynamo libraries. Gets the active document, UI application, and UIDocument.

An assembly element (IN[0]) and new name (IN[1]) are inputs.

It starts a transaction, sets the AssemblyTypeName property to the new name input, and closes the transaction.

The renamed assembly element is output, along with its new name.

So in summary, this takes an assembly element and renames it within a Revit transaction using the RevitAPI. The renamed element is output.