This was asked a couple years ago when Masterpieces were first introduced, and the (O)fficial Answer was "
Sanctioned events will not, must not, use the ‘rebuy’ option."
This thread has some useful discussion about why rebuys are bad for the integrity of the game - even at Regular REL, allowing players to roll the dice again gives players with more money an unfair advantage. It's also incredibly difficult to quantify rules on - do you only allow rebuys if a pack is “valuable?” Who defines valuable? Some players might see $10 as a valuable card, while others draw the line at $100.
If a player opens a pack that contains a Tarmogoyf and a foil Scalding Tarn, they should be thrilled - they got one of the best cards in the set! They can pass the other (along with the rest of the pacK) and keep playing in the event, or take their picked cards, the rest of their current pack and their unopened packs and drop from the event.
Please work with your Tournament Organizers this weekend to help them understand how this rule creates a fair and fun environment for everyone.