If you replace your springs and struts, you will loose warranty on your 'springs and struts' from Ford (Duh!  ). If you use a part however that causes other problems, then that 'other' damage will also not be covered. If you use 'good parts' then you should never,ever have an issue.
Case in point. My Local dealer did not even bat an eye when I lowered my car. But they did sorta ask what I used (in my case the Ford Racing parts). After that is was Oh! OK! I.E. there not Ebay! [burnout]