Managing Custom Packs

Hello,

My friends and I are playing a Yugioh Progression Series and have decided to incoroporate certain cards unobtainable in regular booster packs into custom packs that will allow us to obtain cards released in starter/structure decks, as promos, etc.  Is it possible to change the custom packs once created, if we want to do something like change the card rarities?  I know you mentioned this feature on a Reddit post when you introduced the custom pack feature but the link you included to the pack manager in that post appears broken.  Does this feature still exist, and if so, where can I find it?  Thank you for your help with this!