I know for sure
@DUDEE successfully changes his order from a Pro Boost to a Khaos Boost. He confirmed they had to cancel and resubmit a new order. Others in the last couple of days said that was accurate as well that they have to cancel and place a new order for changes.
But I'm with ya, I'm still hesitant due to my dealer not making me feel confident about it. sucks. If the Boosts weren't so limited, and my dealer didn't already hit their max allotment, I'd tell him to place the new order first before cancelling my original to be safe haha.