When you want to customize the behavior, write as below on your main procedure window. You don't have to rewrite snapshot.ipf.
override constant Snapshot_Resolution = 2 // 4 is default value of Igor Pro
override constant Snapshot_ColorPrint = 1 // 0 means RGB and the others means CMYK
override strconstant Snapshot_Menu = "Graph;-;(Snapshot" // Menu title
override strconstant Snapshot_DefaultFormat = "pdf" // pdf, tiff, jpeg, png, pict, or eps
override strconstant Snapshot_DefaultHook = "Save" // Save, Quit, or Save;Quit