Any way to make a note block keep its note?
Solution 1:
Hitting the block (Left mouse button) makes it play. Activating it (right mouse button) changes the note- this also plays the new note as a preview. When you're playing your song, only use the left mouse button- this will keep the notes the same.
You can also activate note blocks with redstone, using buttons or pressure plates. This can allow you to play several notes at once or even play a tune automatically. Playing the note with redstone is the same as hitting the block- the note will never change.