Symbol overrides are coming to Sketch next week. Check out the latest beta.
I love text overrides in Sketch Symbols, but always missed them for colors and icons.
Then I remembered the Material iconfont has this cool use of ligatures, where you can type the name of the icon and it will draw the actual glyph. Combining that with the overrides, I made an Appbar Symbol where I can customise all text and icons straight from the Overrides panel.
Clearer video: https://gfycat.com/AccomplishedFaintAmericantoad