Anatomy of an Item Code:
It might be a bit more complex than this in some situations or with some more specific items, but this should get you started.
Simple Item Code: (no durability or customization)
16DB = Item ID for Nook Miles Tickets -- change this to what you want from the Item ID Doc
09 = Item quantity (1 more than shown;
00 = 1 Ticket, so
09 = 10 Tickets)
If you change this higher than the max, it will default to 1. So in this example, Nook Miles Tickets max stack is 10 -- if you set this value to
0A (10 in hex), that would be 11 tickets, so you'll only have 1.
Tool Item Code: (durability and single-dimensional customization)
2118 = Item ID for a Fishing Rod
0x = Item
durability, counting up (i.e.
00 is max durability)
0y = Customization color;
00 should be the default tool color, in this example, a blue fishing pole.
So far, no items (that I'm aware of) that have quantity should have either durability or customization.
Furniture Item Code: (two-dimensional customization)
0D79 = Item ID for a Wooden Stool
x = Custom Print value (
0 = No Custom Print;
1 = Custom Print)
CHEATING CUSTOM PRINTS NOT RECOMMENDED (seriously, just use some customization kits)
y = Customization Value 1 (in this case, cushion color)
z = Customization Value 2 (in this case, wood color)
Big thanks to
@Lionheartwolf for clarifying and testing how durability/customization work.
EDIT: I've also quoted this in the main post. I intend to write a basic item code generation web tool to stem the people asking how to edit a code in a basic way, or to make one for specific items, but in the meantime, anyone helping can direct them to this post, or to the OP.