Thanks to Nintendulator emulator, here some cool stuff that I found in the ROM file that you can edit:
Area 0 $4514 - $49D9
Area 1, 2, 9 & 10 $52DD - $5A87
Area 3 & 4 1: $661E - $67B0
2: $6859 - $6DAD
Area 5 & 6 $746B - $7B0D
Area 7 & 8 $5C44 - $65FA
Corridor 0 $4CA7 - $52C9