lowering front end, safe, the right way

Run the correct size tires. Theres a 2" difference between the front and rear tires. If your car has ABS/Traction control (it's an option..not standard) you may get an error code which will turn the system off and display the ABS/TC light in the dash. Tire sizes need to match for ABS/TC to work.

If you want to lower the car (after putting correct diameter tires on the wheels - 245/45/17), then look into a quality lowering spring kit. Keep in mind, you may have to buy some additional supporting mods such as caster/camber plates, isolators, etc to correctly lower a car.

And yes, there is such a thing as lowering a Mustang too much so that handling suffers.

Do the V6's have a rear sway bar? Look into adding a GT sway bar front and rear as well if you want to stiffen up the ride a bit. make sure you get matching bars though. Adding a rear sway bar will make the car more prone to oversteer, so you want to add the matching GT sway bar to stiffen the front up as well and give it proper balance