TREX - Trim Extend. In AutoCAD Express Tools, there was added a command named TREX. Commandline: TREX... Pick to trim or Shift+Pick to extend [Project/Edge/Undo]:
It was a combination of Trim and Extend by holding down the Shift key. That functionality is now part of base AutoCAD. Now you dont need Express Tools to have this option. Its included. Either in Trim or Extend you can use the Shift key to toggle between the two commands. I suggest using the "Select All" option for cutting edge at the beginning to give you the most functionality.