Shifting Note blocks by an octave by using Slime or Honey blocks.

Placing a slime block above a Note block should pitch the octave of the noteblock down by one, allowing for a very bass-sounding note in any instrument. Similarly placing a honey block about a noteblock would up the octave by 1 allowing for a higher note.

(Perhaps honey and slime could both lower blocks, while a different block, such as copper grates, could raise them.)
This would be useful for note block machines. Rather than adding a new instrument it would add more notes themself, allowing for even more complex creations than simply adding more instruments would allow.