As A2A said, nothing changes. You still log in as before and you will see the old card with a zero balance and the new one with the amount transferred over.
My login (ID, password and process) remained unchanged. As did my TPIN and IPIN.
Hell, I didn't even have to add the new card as a payee in my HSBC account. I can continue to make payments to the old (JACC) card number and the credits show up against the new (PM) card.
It was a shockingly painless transition, through and through.
That said, the new user ID based login will be great.
AJ - I'm not sure what you mean by JACC number as login ID. What I have always encountered is:
* Log in using credit card number and password
* If you choose to create a nickname, then you only need to enter the password in future (though the nickname is saved to your hard drive, so logging in from another computer would mean creating a new nickname on that computer)
That means, I had to create a nickname when I got a new laptop six months ago, and haven't had to do anything since. Before that, I had the same nickname for a couple of years.