I have a Dashboard created from a Web map. One of the layers changed in the Web map and now I need to reflect that same change and either edit or build a new widget from that new data source.
Is this possible, or do I have to rebuild a whole new Dashboard now that I have changed or added a layer?
No, you don't have to rebuild it. I'm not sure if you are meaning an op view or dashboard, so I'll include both answers here:
1. Operation View (desktop): Edit the view, and click on the gear icon (Map Settings) above the map. This opens the Data Sources window. The new layer will be present as a data source. Check the box. Then, either edit an existing or create a new widget using that data source.
2. Dashboard (new beta in browser): In the Config of the visualization, click the Change button. Select the layer from the webmap list and click ok.
I hope this helps!