To make items dropped by enemies not refresh their uses when added to the slaying unit’s inventory:
FE7:
-Paste write 02 0A 00 2A 10 D1 24 23 43 43 02 1C 07 49 5B 18 at 0x16174
FE8:
-Paste write 02 0A 00 2A 10 D1 24 23 43 43 02 1C 08 49 5B 18 at 0x16542
This will make dropped items retain whatever uses they had when the enemy died.