Paser State

Hi Guys and Girls.
New to the site and many thanks for that.
Playing around with GRBL by Zap maker and arduino uno with a cnc shield.
What I would like to change is $G View Paser state before it loads.
Need to change the G21 to G20 and the feed rate.
Can do this after it's loaded but a bit of a pain in the butt
Have opened the HEX file but not to sure where to look
And what to do.
Thanks to all