Your asking for trouble, and a major jetting nightmare. A softer spring will allow the needle to left sooner and allow the main jet to flow before the throttle butterfly has fully opened. My opinion is unless you really understand and are very proficient in the flow characteristics of your carb and head just leave that alone and use the needle clip positions for adjustments and different jets to increase HP along with air in and air out.

 

I don't know about cutting or grinding them but I do know that DynoJet supplies new springs with their Raptor jet kit. I've heard that they are a little softer than stock and allow the slide to open a little quicker.