It would be great to be able to "make an icon a symbol and then switch the icon with an override symbol" using symbols as “masks”…at the moment, it’s not possible. There’s a workaround to do something like that is to combine this technique with the one I wrote about for overriding text color in Sketch.

Check the file below!

The plugin changes the way Sketch renders layers on runtime, and since SketchTool does not load plugins, it just renders layers how Sketch itself would do if AutoLayout wasn't installed.

There's a workaround in AutoLayout (find the 'Prepare for Export' menu option) that basically flattens the render and copies the content to a new document.