Thread:~Boggy B~/@comment-33929962-20141205032134/@comment-33929962-20141207122751

You can, actually. Changing your password is a simple matter -- you can find it on your account settings page (open steam, click "steam" on the top left, and select settings), and changing your display name can be done by going on your profile page and pressing the "edit profile" button. Though do note that you can only change your display name, you cannot change your username. This means that while everyone else sees you as your display name, you still need to enter your old username when logging into steam.

And no, you were right the first time. In the event that you create a new account, your old account will still be there, but you cannot use any purchase made by the old account on the new account. And yes, this does mean that you can use your old account just to play Worms Blast and WRU and a new account for everything else, though I imagine this can be quite a hassle.