Well, you have to understand if you want to do it yourself. The data you're trying to edit is not a 1-to-1 equivalent of the tiles you can see in-game in the Subscreen menu. The Subscreen, like many other places in the game, is drawn using commands sent to the PPU, which tells what tile to use and where. The Subscreen menu is drawn in several groups of these commands...
At 1A000, Bank 6, there's a large table of pointers (0x40 pointers) that point to various PPU commands used throughout the game. They don't seem to be in any particular order. Some are for the Intro story, some for the Continue Save Retry screen, some for the Subscreen, some for palette changes, some point to the Cartridge RAM, etc...
At 1A2D3, you have the PPU commands for palette mappings, the A/B Buttons Item boxes, the "-LIFE-" string, and the little icons for Rupees, Bombs and Keys, all in one. At 1A316, you have the "INVENTORY" string, alone. At 1A323, it's for the Current Item box and the inventory box. And so on...