Interesting game, it just hid 12:30am here and I have stuff to do in the morning so I am unable to spend much time looking at the game although I gave it a quick look.
Inside the game itself the only files are some graphics/animation formats, a SDAT sound file (an interesting one if you like that sort of thing) and a font (type 10 LZ compressed, 4bpp, 8x8), it is a nice little one with drop shadows and a few bits of punctuation. The SRL file in there is usually a download play game or a debug leftover and for this I am leaning towards the former, no clues there either as it looks much the same inside it.
This leaves the ARM9 binary and overlays as the potential location. SRL aside none of the binaries are compressed and all the overlays load to the same location. I had a quick look through them and what could have been some shiftJIS was in a few but I do not trust my eyes, Japanese or guesswork at this point (not to mention it was just hex editor shiftJIS decoding). Either way editing binaries is not fun on the DS, as long as it all does not appear in overlay 0004 you should be OK- 0004 wants more than double the space of most others (and sometimes more than that) so memory issues can be hopefully be dodged, you still have binary pointers but those are not so bad to deal with if you understand pointers and memory addressing.
Re: name entry. It has some pitfalls on the GBA and DS (mainly many games use a different encoding) but I so rarely meet people that use it, I should note many DS games use the name from the firmware (crystaltile2 can edit firmware dumps, "DS firmware settings" in any of the windows under the tools pulldown menu, if you want to use it with an emulator) so you can kind of do some stuff here still if you want; you are probably forced to go the high score table and names in save files route rather than memory watching with that but it should allow some semblance of the method to work.