You need to:
1. move the distance between your eyes from the center of your face a random amount
2. move both eyeballs up or down a random amount
This will defeat a vast majority of simple systems. However there are far more sophisticated ones that are slower and require more resolution:
1. mess your jaw line, cheek bones, nose bones, and depth your eyes sit inside your head
Finally the creme de le creme which even identical twins are as different as dogs and cats:
1. get the white of your eyes tatoo'd with new vasculature.
Shouldn't gait play a role in identifying people in addition to facial recognition? Someone was suggesting dropping a small pebble in one of the shoes (or both) to change the walk natural pattern.
What about just a prosthetic nose that it's a bit wider and longer? Blending it in with makeup. I always assumed that's the easiest thing to change that would definitively mess with the metrics.
Sunglasses are a simpler way to obfuscate your eyeball metrics.