To apply Monaco -font to all header_1s in a master document in OO

"If you want all the text that is styled Header 1 in the master document and the subdocuments to have the same style and to be updated together when you make a change, you need to make the change in the template. Changes that you make in the master document only apply to it.

See Page 10, Step 2 in Chapter 13 - Working with Master Documents and also Chapter 10 - Working with Templates."