As daughter of King Michael of Romania, Prince of Hohenzollern-Sigmaringen and of Princess Anne de Bourbon de Parme, we may assume their daughters Margareta, Elena, Irina, Maria and Sofia all have the titles "Princess of Romania, Princess of Hohenzollern-Sigmaringen" in their official registration.
When King Michael decided to cut off the ties with his own paternal and ancestral House, the title Prince (Princess) of Hohenzollern-Sigmaringen is no longer used.
But if Michael, Margareta, Elena, Irina, Maria and Sofia are registered in the civil registry with their formal titulature, then it is not possible to change this because of a daily whim. A father can not change the surname of his adult children because he has got a bad idea in his mind. This means that six requests must have been made to change it in the civil registries. If this was not done, then all five are still Princes (Princesses) von Hohenzollern-Sigmaringen anyway.