Hi guys. I have spent a long time looking for a good way to re-map remote control keys on Android TV without losing on-screen keyboard functionality, and now that I've found it, I thought I should share with everybody else. It hasn't been updated for a couple of years, but it still seems to work well with my Shield on the latest software. It has helped me enable voice dictation using my third-party remote control, and also helped me emulate keys from the Fire TV remote for sideloaded Fire apps. It can also program shortcut keys to quick launch apps. Enjoy!

XDA thread: https://forum.xda-developers.com/android/apps-games/android-tv-control-mapper-keyboard-cmak-t3462028