in Composer 5.0, I want to make the $ key a shortcut to the SMS/MMS app on a theme I'm building. Can someone point me in the right direction. thank you

In composer on the menu bar, Interactivity -> Actions. Far right icon says launch application, hit that and then choose the application to be opened. Then highlight that new entry and hit change event at the top, highlight the on key hit radio button and choose the key to launch your app.