Not sure as to what you are referring to when you say "convert" many of the countries that are in ICAO (in this case the US and Canada) have an agreement of validation of licenses that usually involves less paperwork, exams and you get a validation of the license, they are based on your original license of the issuing country and you have to have that license valid to be able to operate with the validation, now, there is another procedure (and I recommend that you do so) that is to take all the required tests (some might be credited based on your previous certificate) and use the experience that you have already acquired to get an independent license so that you have two certificates instead of a validation based on one certificate. You will not lose your FAA certificate when you obtain a certificate from another CAA, I have three different ICAO licenses independent from each other.