I would like to know if it is safe to edit the config.txt file on a Retropie image to change the
arm_freq=1200 since it will be running on a R-pi 3 model B?
The Raspberry Pi 3 Model B starts at 1.2Ghz regardless of what
/boot/config.txt says. Here are the results of my clock speed files on my Pi 3 with
config.txt not edited from a fresh card:
sudo cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq 1200000
When not under load:
sudo cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq 600000
When playing music with
sudo cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq 1200000
You do not need to change
/boot/config.txt if you want your Pi 3 running at 1.2Ghz, if you want to overclock it, that is a whole different question. Hope this helps.