You can use key combinations like CTRL B and CTRL E to do this today however you cannot use single key strokes as those could not be discerned from wanting to enter the letter b into a data field like Code or Description or Name etc. You define these under keyboard shortcuts - Support - Define Command Shortcuts.
If you are using TBC v5.3 there is also the new Command Line that you can pop up using the Toggle Icons at the base of the screen, from there you can run commands like Break Line, Join Lines etc using predefined keyboard shortcuts that function in the Command Line only - in that case T enter will run Trim, BR will run Break Line, J will run Join Line etc. there are around 25 commands supported in the Command Line in TBC v5.30.
Let me know if this helps