Yes, I'd also recommend a tuner and to leave the global spark alone. Global spark mean that change is made EVERYWHERE. Under all loads, temps, conditions period. IE:Think of it like base timing on an older car with an adjustable distributor housing. Advancing it there will give a higher base number to add the mechanical advance to.
So lets say you do add 2* everywhere...it's quite possible, even likely, the knock sensors will pick up knock and the pcm will just take that ignition advance back anyway.
There are times when more advance can be used, heads, cams, etc to help make up for a loss of cylinder pressure below peak torque but your engine is way too stock for that concern just yet.
All that said, you have to datalog these things and then a Mustang brand load bearing dyno would be best to go up in 100 rpm increments at a steady state to tweak the whole ignition advance map.