Copying to your ROM a song available on the Forum

So I took c54195-c54c34 (header) instrument index and pasted to FF0000 (header)
then at c503e2 (header): bf953fc5 change to BF00FEFE
changed C53E5E (header): 55 to 56
at C54195 I put in 2DF3F4
I pasted the song data to F4F32D and set the pointer at C54195 to 2DF3F4
Then I copied the instrument data at FF0AA0

Ok, first three steps are good. You got a good understanding of the effect of an header. For 4th and 5th steps, if you put the song data at $F4F32D (header), pointer will need to point at $F4F12D (because you use a header), so pointer value at $C54195 will be 2DF1F4.

Finally instrument data is adding $20 bytes at $FF0AA0, so you instrument data will cover from $FF0AA0 to $FF0ABF. I think you got that right.

There isn't more than this to it except referencing song $56 in an event or in code, if you still got issue, something in the process is not done correctly. You might want to remove the header and re-attempt this, header are confusing and they serve no real purpose. If all fails, I could look at your ROM Sunday and find your error, you've done most of the process correctly from what you post.