After you file

That is correct.  If you do not need to report K-3 income then you do not check box 16.  However, if you file your return and receive a K-3 for foreign income at a later date you will need to amend the return.  To amend your return in TurboTax you can follow these steps:

1. Sign in to TurboTax
2. On the home screen, scroll down to Your tax returns & documents and select the year you want to amend
3. Select Amend (change) return, then Amend using TurboTax Online
   • If you're told to amend your return via TurboTax Desktop, follow the steps for TurboTax CD/Download below instead
4. On the screen OK, let's get a kickstart on your amended return, select the reason(s) you're amending and Continue
5. When you reach Here's the info for your amended federal return, select Start next to the info you need to change
6. Continue through the screens, make the changes you need to make, and carefully answer the remaining questions to finish amending your return

For more information on amending returns, see the link below:

How do I amend my federal tax return?

@taxlady28