STEP 1: Open your storyboard in Xcode 8 and choose an initial device view. Make changes as you normally would.
STEP 2: Once you have completed your changes, select the storyboard -> File Inspector -> Opens in -> Select ‘Xcode 7.x’.
STEP 3: Select ‘Save and Close’ when prompted
STEP 4: Your storyboard changes will be saved, and your storyboard will function as it did pre-Xcode8.

When you need to make other changes to the storyboard file, follow these steps again.