In orders where it's customary for monks and nuns to adopt new names, do they also legally change their name? Or do they still legally have their birth name? Couldn't that pose complications later on? Is there any scenario where they might still need to use their old legal name even after adopting the religious name? Also couldn't it cause some complications since multiple monks or nuns might have the same name? I can think of three different nuns with the name Teresa of Jesus.
I'd imagine that in the Vatican, the Holy Father is legally Benedict XVI. But when he chose that name, was his legal name insofar as his German citizenship was concerned also changed to Benedict XVI, or is he still Joseph Ratznger? The question applies to all popes of course, not just Benedict. Was John Paul II still Karol Wojtyla and so forth?