Fyi, Cryptic is going to add the ability to downgrade a higher grade duty officer into 3 random lower grade duty officers. For example, you will be able to downgrade a very rare purple duty officer into 3 rare blue duty officers, or a rare blue duty officer into 3 uncommon green duty officers.
A single very rare purple duty officer can be converted into 27 common white duty officers. Once the patch goes live, chances are the price of all green, blue and purple duty officers will go up as people grab cheap higher ranked doffs. In other words, it is now time to stock up on cheap green/blue/purple duty officers in the exchange while their prices are still low.