I know lot of you still wonder how do you change your ingame name in ARMA3.
Today I will post the tutorial on how you exactly do it.
Step 1: Open Run by Windows+R, enter lusrmgr.msc and hit OK to open Local Users and Groups.
Step 2: Open the Users folder, right-click a user and select Rename in the menu.
Step 3: Type a new name in the name box.
Restart your PC, Run the game and you will see your changes in game.
Please note changing name in windows will change the name in game and not in steam profile. You will also loose all your keybindings, video and audio settings.
You will also loose your saved loadouts in game.
I hope this has helped you.