WAB 2.5 - as an experiment, I copied the "Simple" widget from the "samplewidgets" folder to the "widgets" folder and made the necessary edit to config.json. I then created a new application and added the "Simple" widget to the app. I then edited the Widget.js file (replaced the word "very" with "ridiculously"), then refreshed the app. The change did not display. I then cleared the browser cache, edited the app by deleting the widget from the app, saving the app, re-adding the widget, and saving the app again. The change did not display. I then added the widget to a new application, and that's when the change showed up in the widget.
During development, you constantly update the interface and modules (unless you're THAT talented), so how do you edit a widget that's under development? I guess I can go into "server/apps/appId/widgets/customWidget" and edit files there, then transfer the edits when I've finished development back to the widget folder in "widgets", but that just seems like a backwards way to do development.