transpose the input

[Federico Bruni]

Hi,

I'm sure this has been asked before, but probably I'm using the wrong 
keywords.
I'd like to *transpose the input* of a piece to a different pitch (for 
example from g to d).
I know that I can use \transpose to change the output. But I'd like to 
change the input.

There's any tool in the lilypond package which can accomplish this task?
Thanks in advance,
Federico