Do I have to change the input power from 100 Volts AC to 240 Volts AC (or vice versa) manually, or is my unit auto-sensing/auto-switching?
Yes, the units you see below have auto-sensing/auto-switching powersupplies. You just need to get the right AC plug for the country you're in.
HarmonyControl Guitar (discontinued)
VoiceLive 2 / VoiceLive 2 Extreme Ed.
VoiceTone Create (discontinued)
VoiceTone Create XT
VoiceTone Correct (discontinued)
VoiceTone Correct XT
VoiceTone Harmony-G (discontinued)
VoiceTone Harmony-G XT