K40 Touchscreen for Smoothie

K40 running Smoothie on an SKR v1.3 - would like to use something like a Nextion to create a touchscreen for the control panel. Is it possible to send keystrokes to the SKR, possibly via serial or some other method? I’m looking to send things like G28, M999, move commands - in addition to the ALT+S and ALT+R.

Forgive me if this has already been answered or is in the wrong place.