If you have already paid for the Deluxe for Fed and state but haven't efile and would like to upgrade to live Tax advice can you do so and only paid the difference?

Yes, you can add Live after you have paid for TurboTax, but have not yet Efiled.

 

Click the 'Live Tax Advice' icon in the upper right corner while in your return.

 

Here's more info on How to Schedule a Live Review.