The main ram should be mirrored four times in the 2000000 region, so the only interesting area is from 2000000-23FFFFF as the rest is the same as that anyway.
It's probably easier to search for data that is loaded early on and kept in memory at all times, something that you can easily expand. Fonts are generally pretty well suited for that.
If you can find the functions that the game uses to load a file into memory, you could also put your code into its own file and just implement a small loader function somewhere (overwriting a few strings that you can put into your new file then, for example). That's what I usually do.
What do you mean with "ldr that location"? Loading an immediate (ldr r0,=address) or loading data (ldr r0,[r0])?