Can API subscribe users to two email lists at once?

Hi. First time here with a question to ask.

About 2 years ago, I paid a consultant to help me add Constant Contact API code to a user registration web form. It signs up new users to a list that sends a one-time Welcome email.

Now we would like the signup to immediately send the Welcome email PLUS add the user to a weekly email campaign. Is that possible to do in one action? Can we code two separate list requests triggered by a single action in our registration form?