The "8116438A 42AC" is a gameshark code. The 0x81 is an
op-code that says: every frame, write 0x42AC at RAM 0x0016438A (equivalent to TLB 0x8016438A). So, every frame the gameshark will change whatever value is in memory at that address to 0x42AC. At some point in time during the game, that address contains the value for Link's Up-B.
If you want to find where on the ROM that value is coming from, that's a lot harder. If you're lucky, the data will be stored on the ROM uncompressed. You could use Nemu/Bizhawk/any emulator that lets you look at the RAM while running the game, and look at 0x8016438A when you think that that address will contain Link's data for up-b. (You can actively change the value at 0x8016438A so see if it really is link's up-b). Open the ROM up in a hex editor. Copy the data around 0x8016438A and search in the hex editor to try to find that data.
If it's compressed (ie, you can't find that data in ROM with the hex editor), good luck.