To offset keys:
Select the frame you want to start adjust from and click “Set start”. Select a end frame and click “Set end”. Now reposition, rotate or scale your objects and then click “Adjuts” to offset the keys between start and end.

To prevent create new keys and save the transform change in the last key: Use the checkbox to start use this mode. Work as you normally do and you will notice that any new keys will be moved to the closest previous key instead.