I used the ones from the baqck for the front ones... No problems... The little color coded plugs on mine don't match up, but everything still works great anyways.
Switch them if you want, tell you the truth, I don't really care what you do. Call a ford dealership and ask what the part numbers are for a front o2 sensor and a rear o2 sensor. Compare the part numbers then find out for yourself if they are the same.