I have some great news to share: I found all the character affinity codes, and confirmed with Lin and Elma already!
I also found codes for the vast majority of probes.
Now the ugly news: it turns out that INDIVIDUAL items are not stored in fixed memory locations. Instead, the memory addresses correspond to item SLOTS (e.g. first material slot, first precious resource slot, first probe type slot, etc.), and the address contains data about the item ID, item type (I think), item count, and 3 bits that I don't know what.
This explains why
matrixsoul was reporting that the precious resources codes were incrementing different items on his save -- he acquired the resources in a different order.
I'll need some time to figure out some key item IDs, and re-design the UI and code structure accordingly.
Also, since this game has so many items, I simply don't have the time to map out all possible IDs. Therefore, I can also use some help, who would be willing to poke different memory IDs and note down the corresponding item. I'll update the first post with details later.