Writing names of angels/verses on the Mezuza

Igros Moshe (YD II #141.1) Question: Is it permitted to write the names of angels and verses on a mezuza? Answer It states in the Sefer Yeraim that it is a widespread custom  to add the names of angels  for the sake of protecting the house. The problem is that it looks like a amulet for the purpose of protection of the house and not a mezuza but  there is no problem of baal tosif. Rashi clearly holds that a mezuza ptrotects the house and therefore there is no problem adding protection as long as it doesn’t violate baal tosif and doesn’t look like an amulet.