For starters, you'll void your warranty. Other than that, there's no difference in the LED modules used by the Apprentice and Sentinel lines, so it's a simple enough swap.
As pointed out to me earlier today, the VA uses 2 diodes, which, as the batteries drain, will cause one to fade and the color to become more red.
It was suggested that if you're going to use VA, switch to Li-Ion batteries and a Buck Puck to keep the power between the diodes even as the batteries drain.
And then there's that. Not a huge deal, though.