Apparently the Apprentice can be redeemed so I would say the use of a Jedi blade would be in order. Plus if he is supposed to be "undercover" and all of his missions are covert then what better way to gain trust by disguising himself as a Jedi.
Also if the hilt will be customizable then I wouldn't doubt that the crystal would be.
I think the upgrades will be similar to lightsaber upgrades in KotOR 1 & 2.
I QUIT LF!