I did go through with the password change and my PIN still works. I use it everytime I log in onto the new app and on the new dl.com vs using the new password. I see a lot of complaints about the new password, but yet IME, the login process is the same (SM#, PIN, last name). That said, over the phone is the only time I have had to use the password. So luckily I went through with the change long before I needed to speak with an agent.

Sorry OP that you went through this. As we all know well, the system still is broken. But the moral of your story is correct.