You do have to preview again, then click "Reload All".
I agree with an option to combine "Reload All" into the preview button - I often click Preview, go back to my NWJS window, and don't realise that I haven't clicked "Reload All", even after months of doing this!
There's this page that has shortcuts, apparently SHIFT+F4 or SHIFT+F5 will do it.
I'd love to change this into a 1-key shortcut, but hey maybe AutoHotkey could help there.