I just had my Headlights out and put in some of those switchback LED blinker bulbs. You know, the 2012 Mustang's headlamp housing is the same on both HID and Non-HID cars. The ballast is actually inside the Headlight housing and all you do is plug in the power for them and the blinker cord. I know there will be issues with the bulb monitoring system and maybe the Hi-Lo beam stuff but maybe the ST's have a separate Halogen High Beam bulb. Once the cars actually come out, maybe someone can look into this and see if they can be wired to work in a regular Focus.
Just a note: In case anyone puts those "50 watt 6 ohm" resistors in to simulate the load of a regular lamp for LED replacements, be sure to mount them to a flat metal surface as they get really hot if say you leave your emergency flashers on for a while. I ended up using an old computer system CPU cooler aluminum finned heat sink and modified it to mount inside my fender area and then screwed the resistor to it with that heat sink compound as to help dissipate some of that heat. Before I did that, you could not touch the resistor without welders gloves on but after the mod, the resistors were hot but you could touch them bare handed without getting blisters.