Where and how can I find the relevant documents of name changes?

For name changes before 1893 find relevant information int he book Századunk névváltoztatásai (1800-1893) Bp., 1893. Considering the time period 1894-1913, the Interior Ministry holds highly incomplete holdings. The Interior Ministry did not provide files originated after 1913 to the National Archives of Hungary. For the customer service’s contacts click here.