回複:I believe so. But my lawyer has problem with it
There is no law or regulation saying you have to inform CIS. As a practical matter, do it. Some interviewing ofiicer at 245 interview asks "did you notify the CIS", you don't want to get into the argument with the officer that it is not required.
You can send the letter yourself as long as you know the I-485 filing receipt number. It's up to you.