assign mouse cursor to mouse modifier

[vala]

Hi all!
Searched but found nothing... also, not sure to ask this in the right forum...
Anyway, here's my question:
I attributed a mouse modifier option+click to the "split items" action, how can I make appear a specific cursor when the mouse pointer is on a media item and the option key is pressed? I'd like that in this case, the pointer became a razor blade or something similar.