Simplify the following text for a Grade 9 native English-speaking person.
Original: : \* 1949 â '' 2001 Imperial Household Agency was the new name of Imperial Household Office ; and the Imperial household became an external agency of the Prime Minister 's Office .
Simplified: In 1949 , the name of Imperial Household Office was changed to the Imperial Household Agency . In this way , the Imperial Household became an external agency of the Prime Minister 's Office .