I am not sure what you are trying to do here, but if you want replace the PIX with an ASA you can use the PIXtoASA converter to translate the config.

Depending on your routing setup and available IP addresses, you can then deploy your ASA in parallell with the production PIX, and at one point redirect the internal default route to the ASA.

Any current sessions will have to be re-established, so a minor drop in production should be expected.

Harald.