Don't ask me how I know but make sure you need to shorten wires before you do it. It doesn't take much to raise the mast and check to see if you can get the mast rake you want, with the additions.

In many cases we rake the mast much further aft today, than when the boats were designed or the rigging you are using is not standard.

It really sucks when you shorten everything and then have to add an extender to get the mast rake you want.