Can previously inserted Porex jaw angle implants be shaved down?

In my experience, these implants are very difficult to modify especially if they are modified in place without removal. The easiest approach is to remove the implants, modify them and then replace them. This would likely be just as invasive or more so than your initial procedure.

It is very hard to give you good advice without clinical exam. However, Porex implant could be shaved and properly reshaped if accessible. You should discuss this option with a surgeon who will perform chin implant reshaping . Good luck.

It would not be easy because if the implant get loose or infected it may need to be removedusualy this implants hard to separate once the soft tissue grows around themmay be a larger procedure than initial insertion

Yes, you can alter the Porex. It is not simple dependent upon 'where' you want to change the shape/position; but ask the surgeon who is doing the chin alteration.