Thanks to the new inventory system implemented in Ocarina of Time 3D, it's possible to trick the game into allowing you to equip adult items as child and child items as adult.
In the item menu there are twenty slots for storing items and four slots for equipping items for a total of 24 slots. Normally there are only 22 items that you can get to fill these slots. However, by using RBA to write bottles into the ice and light arrows slots, you can actually fill all 24 slots.
Now when you get an item as what the game will do is it will go through your item slots and put the new item in the first available slot from left to right, row by row. However, if all of the 20 slots for storing items are full, it will then put the item on one of the slots used for equipping.
now if you are child Link and you collect an item that is only meant to be used by adult Link and all 20 of your slots used for storing are full, what the game will try to do is swap the item you are not supposed to have with bombs. However, if you do not have bombs or if you already have bombs in one of your 4 equippable slots, then the game will attmpt to switch the item you are not supposed to have with bombchus. If you do not have bombchus or you already have bombchus on one of your 4 equippable slots, then the game will no longer try to swap the item you are not supposed to have equipped into your 20 storing slots.
You can also get items you are not supposed to have equipped by duping bottles over those items, putting that into one of the 4 item slots and then collecting that item. However, when you enter a loading zone, the game will check if it can swap that item with an empty slot or bombs and bombchus. However, if you followed the criteria for inventory overstuffing above, the item will not be swapped out. Therefore you can swap items freely and still keep the items that you are not supposed to have so long as you do not enter a loading zone with an empty space, bombs, or bombchus in you 20 storing slots.
The easiest way to get a total of 22 items is to collect the following items:
And then perform Reverse Bottle Adventure with the following items on the II Button: 1. Hookshot - Bottle in the Ice Arrow slot 2. Lens of Truth - Bottle in the Megaton Hammer slot 3. Red Potion - Bottle in Bottle #4 slot 4. Fish - Bottle in the Hover Boots slot
Finally, perform Bottle Duplication over Bombchus to get rid of them.
With inventory stuffing, it's possible to equip No Mask (3D's version of SOLD OUT) to the II button allowing for more Reverse Bottle Adventure possibilities.
To start, you'll need to have completed the Forest Medallion, and have two masks unlocked but haven't traded at least one mask yet.