It just determines the base tune. No impact for an n/a setup running the turbo base tune but the turbo setup can't run an n/a base tune, hence the reason I said to select the forced induction selection.
Note the PiMPxs requires high impedance injectors only. So you're fine for now as the stock n/a injectors are high impedance. Once you go turbo you'll need to buy larger high impedance injectors instead of running the stock turbo injectors.
On 92 Mustangs the air bag wiring is wrapped in the factory ECU wiring. When I changed to a PimpX I drilled a hole in the firewall just for the airbag wiring so it not longer is wrapped up with the ECU wiring on my 92 Mustang. A few people mentioned when they changed out the ECU the air bag light flashes- usually the cause it the wiring was left out