#!/usr/bin/perl
use strict; 
use warnings;

my @array = <DATA>;
foreach( @array ){

s/G1/G0/ if(m/F30000/);

print $_;
}

__DATA__
G1 Z0.500 F30000
G1 X13.379 Y-36.065 F30000
G1 Z0.100 F30000
G1 E76.00000 F300000
G1 X13.760 Y-35.411 E76.37759 F2400.000
G1 X14.123 Y-34.917 E76.68356
G1 X14.170 Y-34.656 E76.81576
G1 X14.133 Y-34.485 E76.90331
G1 X14.038 Y-34.357 E76.98253
G1 X13.947 Y-34.323 E77.03113
G1 X13.673 Y-34.283 E77.16949
G1 X13.078 Y-34.094 E77.48100
G1 X13.163 Y-33.464 E77.79807
G1 X13.321 Y-33.182 E77.95920