C:\Program Files (x86)\arduino-1.6.10\hardware\tools\avr/bin/avrdude -CC:\Program Files (x86)\arduino-1.6.10\hardware\tools\avr/etc/avrdude.conf -v -patmega328p -carduino -PCOM21 -b115200 -D -Uflash:w:C:\Users\per\AppData\Local\Temp\builda0905d717cd3fb20c5f6c59067701315.tmp/serial.ino.hex:i
they first need to download AVRDude?
Will this method still work if I tell them to put the .hex file in a certain location and send them the command line?
For your purposes it might be more user friendly to find some kind of a GUI wrapper application for avrdude that will allow the port to be selected from a menu as the Arduino IDE does. I'm pretty sure I've seen people refer to something like that here before but I don't remember the name.
"C:\Program Files (x86)\Arduino\hardware\tools\avr/bin/avrdude" "-CC:\Program Files (x86)\Arduino\hardware\tools\avr/etc/avrdude.conf" -v -patmega328p -carduino -PCOM13 -b9600 -D -Uflash:w:C:\Users\mike\AppData\Local\Temp\arduino_build_221325/OpenLCD.ino.arduino_standard.hex:i