I got some answers from Gamefaqs.
A poster called Orsted replied:
1. The WAV file you're trying to replace (original song will be kept if left empty)
2. Loop starting point
3. Hexadecimal mode (in terms of bytes)
4. Song ending point
5. Second(s)
6. Data save location (do not choose the game install folder)
7. Create a song title file for the Touhou phonographAnd a poster called Rakesus edited the image I used, so I'll post it too:
Now let's hope I can use it right.