Lincoln/Merc is still Ford, it wouldn't make much of a difference between them. Anyway the dealer CANNOT (I think legally) fully void a warrenty for springs. They may not cover the replacement of your struts/shocks due to premature wear (from a drop). They can get away without covering anything suspension due to suspension mods. But if your engine blows, they have to cover it (unless its your fault).
About cutting springs, I've never done it, never will and highly discourage it. Springs are cheap enough anyway ($200 isnt out of reach)
Sorry to hijack but,
Shadowrunner,what size wheels are those? I have SVT springs in my car and have about the same size fender gap as in the picture you put up, but I have the stock 16's.