This is a useful set of hex addresses to know. By changing these pairs of bytes, you can change what items the Great Fairies upgrade. If you're testing out a hack, this is especially useful for being able to load in a fully completed save and then downgrade your items (for example, going from a red tunic to a blue tunic).

Original Bytes:

==Waterfall of Wishing (Near Zora's Domain)==

GIVE: 03/48D3: 0C (Boomerang)
GET:   03/48D7: 2A (Red Boomerang)

GIVE: 03/48E3: 04 (Shield 1)
GET:   03/48E7: 05 (Shield 2)

GIVE: 03/48F3: 16 (Empty Bottle)
GET:   03/48F7: 2C (Green Potion)

==Mysterious Pond (Golden Pyramid)==

GIVE: 03/4908: 3A (Normal Arrows)
GET:   03/490C: 3B (Silver Arrows)

GIVE: 03/491F: 02 (Sword L3)
GET:   03/4923: 03 (Sword L4)


Some useful bytes to know:
$49 Sword L1
$01 Sword L2
$02 Sword L3
$03 Sword L4

$04 Shield 1
$05 Shield 2
$06 Shield 3

$1B Power Glove
$1C Titan Glove

$22 Blue Armor
$23 Red Armor

$0C Boomerang
$2A Red Boomerang

$16 Empty Bottle
$2B Red Potion
$2C Green Potion
$2D Blue Potion

$0D Magic Powder
$12 Lamp
$0A Hookshot

If you do end up replacing the arrows or the sword, refer to this thread:
Give Silver Arrows/Sword L4 Chest Messages