I started this same thread about 2 weeks ago and got no replies smh.
But I am also very interested in this but found while doing research that a flash bleeds into the photos because there is usually no photo diffuser on the replacement back panels.
Installation is usually easy because they send you the star tool. I am still very interested in this, as I only wear a bumper and protective film on my 4s so a replacement door would really stun those who look at my device. Besides that there's really no other reason to change the back panel.