Do ski tourers have to register for the evening tour? Nope - you can always start your ski tour on Wednesdays in Nesselwang at the Alpspitze.
Are there specific times you're allowed to be out and about? Nope ;) Just make sure you DO NOT walk on the slopes, but use the marked path.
Do you need headlamps? YES! The floodlights are only on until 9 p.m. and only up to the middle station. So if you want to get down safely, you should definitely bring a headlamp with you on your ski tour at the Alpspitze in Nesselwang.