On my 2002 GT I ran a 125 shot of NOS NOSZLE direct port gas without a tune with no issues...NOS specifies that you run it on a stock tune. I had a few other safety things though...colder plugs (as specified by NOS), NOS window switch, FPSS, Wideband, FP gauge, KB Boost a Pump, Plasma Booster...
Sure it is safe...but don't be stupid with it and follow the recommendations of the manufacturer to the letter. Best of Luck!