To what extent is what was narrated concerning the virtue of saying "O Creator" (Ya Bari') 100 times every Friday authentic, and to what extent is it valid to generalize this virtue to all of Allah's Beautiful Names?

There is no basis for this statement in Islamic law. Dhikr (remembrance of God) using only a single name is not prescribed. Islamic law recommends dhikr with complete and meaningful phrases, such as "Lā ilāha illā Allāh" (There is no god but Allah) and "Allāhu akbar" (Allah is the Greatest), and the like. There is no mention of dhikr using a single name, whether explicitly stated or implicitly understood, in the Quran or Sunnah, nor from the predecessors of the Ummah, nor from its prominent, exemplary figures.