Replacement of items handed over by characters
Note: stuff that appear as a collectable sprite is tricky to change (e.g., the thrown items - earth medaillon, flippers, or the digable flute. To get an idea, refer to the doc in  
Zip: http://bszelda.zeldalegends.net/stuff/Con/random_special_treasure.zip

Magic mirror by old man:
0f/6a00:1a -> desired item (hex 1a is chest item dec 26 in HM)
e.g., moon pearl is hex 1f (dec 31)

Note: there's a check whether you already have collected the mirror. To not let the old man reappear in the cave change at  
0F/6910: af 53 f3 7e c9 02 -> to the ram location of the new item aquired by the old man (7ef353-02 is magic mirror).
E.g., moon pearl: af 57 f3 7e c9 01 (since 7ef357-01 is the moon pearl)


Bug-catching net:
03/39C7: 21 -> desired item

check if you already have collected:
03/0d7f: AF 4D F3 7E -> new ram location
(7ef34d is the net)

Pegasus Boots:
05/F1FC: 4b -> new item  

check if you already have collected:
02/F177: AF 55 F3 7E -> new ram location
(7ef355 is the boot ram location)