I'm going through the same thing at the moment, but I do intend to tune the PFC myself.

I wouldn't drive on the existing tune if it was me, or at least I would drive carefully.

To reload the default tunes you need to go into ECT on the handset and go to initialise, then select yes, then turn the car off then on again.

The power fc default tune is for an STI so you'll need to set your injectors up for the 380cc ones your WRX has by setting the injectors to 117%

I would be best to take around 3-5 degress of advance out of the whole map as well.

The default map is rich, and the ignition is very aggressive.

It only takes 5 minutes to physically install a Power FC, so you could drive to the tuner on your existing ECU and swap it in the car park, or just hand it them on the day.