Is there a way to set Sound Balance permanently for MacBook?
I once had the same problem and resolved it.

Issue the following commands.

$ mv /Library/Preferences/com.apple.soundpref.plist /Library/Preferences/com.apple.soundpref.plist.backup

$ mv /Library/Preferences/Audio/com.apple.audio.DeviceSettings.plist /Library/Preferences/Audio/com.apple.audio.DeviceSettings.plist.backup

$ mv /Library/Preferences/Audio/com.apple.audio.SystemSettings.plist /Library/Preferences/Audio/com.apple.audio.SystemSettings.plist.backup


Then select whatever preference of sound settings you want and restart the MacBook.