Don't Start Cutting
Before removing material, you should try something non-destructive first.
Compress it using a long 3/8" bolt or threaded rod plus a couple of washers and nuts. Don't take it all the way down; just get it to half it's current length or a bit less. Then leave it for a day or two. The spring should 'set' about 1/2" shorter.
This worked quite well on the Wolff Browning Hi-Power spring that I put in my CZ75.
Hope this was of some help.