[NES 6502 ASM] Modifying Loaded / Stored Value At Address Not Available As An Address?

I have been wondering if this is possible, like if there is a way to do it that requires a certain method.



You can see where I have highlighted in red, the value in question. It is not stored as an address, except the memory location it rests on at 0xEFCA as a reference to the address in the main memory (2KB Internal, 0x0000 - 0x07FF), which are values, not instructions. The instructions are held at 0x8000 - 0xFFFF (assembly).

There are 3 bytes at EFCA... 99 is the opcode (STore Accumulator - Absolute,Y), 1C & 07 is backwards for the address. However, it is not possible for anymore bytes to be stored on the line, but 03 remains unable to be modified.

As I aforementioned, 03 is a reference to the "value memory". So, can 03 only be modified by a direct RAM write? It would be better if it could be modified with a Game Genie code, so you could have a compare value to change the value only when it is the compare value, preventing freezing and other unwanted effects.

For some reason, I think I'm missing something, but would like someone else's input. Thanks for reading.