To reuse a storyboard, could I simply copy it from one project to another project (then make modification to the storyboard as required)?
Yes you can, just make sure they are selected as your main storyboards as per image below.
As @Muhammad said you can and it is very simple!
It's simple. Just follow these steps:
Cheers.
Method 1
Select the View Controller in the storyboard and press Command + C to copy. Then press Command + V to paste in the second storyboard. Check the document outline to see where it was pasted to.
Method 2
Right click the storyboard file in the Project Navigator and select Open As > Source Code. Scroll down the XML code until you find your View Controller. It will look something like this:
<!--My View Controller-->
<scene sceneID="tne-QT-ifu">
...
</scene>
Copy this and paste it in the second project's storyboard file.
Notes