No, not in the online program. You would need to create two separate accounts or you will overwrite everything on the first scenario when you enter the second. You can use the same email address for the accounts, but they need to have distinct usernames.
You can run as many "test" returns as you like using the desktop version of the software. If that is something that you might be interested in, then you can get more information at the link below -
https://turbotax.intuit.com/personal-taxes/cd-download/deluxe.jsp
