is this actually achievable with arduino?
Yes it is quite easy.
What you need is a look up table. This is just an array.
The index of the array ( the position of an entry in the array ) is the note you want to intercept, the contents of the array is the note number you want to map it to.
Then read in a note on or off message on say channel 1. Then run the note number through the array and output it on channel 9 percussion.