My idea is for simple switching from liveTV to catchup (if the channel have catchup source). If you watching liveTV and the channel have setup catchup source server, when pressing arrow left automatic to switch on catchup source and rewind back with 15 minutes for example.
Also if possible a simple rewind back button on the menu (if the channel have catchup source) to be added (jump back with 15 minutes for example). Rewind forward button in the menu when watching from catchup will be good too. When watching from catchup less than 15 minutes back from current timestamp rewind forward button can switch from catchup to liveTV source automaticly.
Now left arrow is used to switch to previous watched channel, but for this can be used key 0 (it do nothing now).
Also for user friendly is it possible to be add menu option (on/off), when watching from catchup source, icon to be shown on screen (small clock in up left or up right corner for example), so will know you are not watching LiveTV but archive in the moment.