Sorry for the thread necromancy. I took STN's work a little further and I believe I have what should be close to, if not, all the item codes below.
Also to save yourself the frustration of trying to figure out why this isn't working, a tip. This table uses item slot 1, your Potions and will replace them. Before you start, auto sort your inventory and buy some potions if you don't have any already. Load up CE, set the slot 1 ID to 0 (potions) and qty to 99 or some other, non-zero number.
Then you should be able to modify the id to anything else. If you did it wrong, the ID won't work, you won't be able to use it for customization or in the case of the sphere grid, you can "use" it but nothing happens.
ID Item
0 Potion
1 Hi-Potion
2 X-Potion
3 Mega Potion
4 Ether
5 Turbo Ether
6 Phoenix Down
7 Mega Phoenix
8 Elixir
9 Megalixir
10 Antidote
11 Soft
12 Eye Drops
13 Echo Screen
14 Holy Water
15 Remedy
16 Power Distiller
17 Mana Distiller
18 Speed Distiller
19 Ability Distiller
20 Al Bhed Potion
21 Healing Water
22 Tetra Elemental
23 Antarctic Wind
24 Arctic Wind
25 Ice Gem
26 Bomb Fragment
27 Bomb Core
28 Fire Gem
29 Electro Marble
30 Lightning Marble
31 Lightning Gem
32 Fish Scale
33 Dragon Scale
34 Water Gem
35 Grenade
36 Frag Grenade
37 Sleeping Powder
38 Dream Powder
39 Silence Grenade
40 Smoke Bomb
41 Shadow Gem
42 Shining Gem
43 Blessed Gem
44 Supreme Gem
45 Poison Fang
46 Silver Hourglass
47 Gold Hourglass
48 Candle of Life
49 Petrify Grenade
50 Farplane Shadow
51 Farplane Wind
52 Designer Wallet
53 Dark Matter
54 Chocobo Feather
55 Chocobo Wing
56 Lunar Curtain
57 Light Curtain
58 Star Curtain
59 Healing Spring
60 Mana Spring
61 Stamina Spring
62 Soul Spring
63 Purifying Salt
64 Stamina Tablet
65 Mana Tablet
66 Twin Stars
67 Stamina Tonic
68 Mana Tonic
69 Three Stars
70 Power Sphere
71 Mana Sphere
72 Speed Sphere
73 Ability Sphere
74 Fortune Sphere
75 Attribute Sphere
76 Special Sphere
77 Skill Sphere
78 White Magic Sphere
79 Black Magic Sphere
80 Master Sphere
81 Lvl 1 Keysphere
82 Lvl 2 Keysphere
83 Lvl 3 Keysphere
84 Lvl 4 Keysphere
85 HP Sphere
86 MP Sphere
87 Strength Sphere
88 Defense Sphere
89 Magic Sphere
90 Mdef Sphere
91 Agility Sphere
92 Evasion Sphere
93 Accuracy Sphere
94 Luck Sphere
95 Clear Sphere
96 Return Sphere
97 Friend Sphere
98 Teleport Sphere
99 Warp Sphere
100 Map!!!!!!
101 Rename Card
102 Musk
103 Hypello Potion
104 Shining Thorn
105 Pendulum
106 Amulet
107 Door to Tomorrow
108 Wings to Discovery
109 Gambler's Spirit
110 Underdog's Secret
111 Winning Formula
I know this post is old, but I found the script useful, but also adjusted it for the first four item slots, as well as adding a dropdown list for the items so looking up the value for items isn't necessary.
Edit: Updated to the first 32 slots, and added a dropdown entry for "Empty".
Updated to the first 64 slots, and added number of encounters. I haven't verified how it effects Blitzball prizes, but setting # of encounters entered to 700 did make Aeon stats go up.
Update: added a counter for the number of Tidus' overdrives. Despite what some guides say, his overdrives unlock from the total number of overdrives (10, 30, then 80), and not necessarily the previous overdrive. There is only one counter for the unlocks.
Item ID is two byte instead of a single byte. Second byte is always hex 20 when there is an item, and 00 when it is empty. Treating it as a single byte causes wonkiness when going from empty to having an item, and vice versa. Adjusted item IDs to 2 byte hex to fix this, and expanded list to the first 96 items.
Edit: Expanded to 128 items, and grouped them by 32.
Edit 2: included a counter for the number of times Rikku has stolen.
