Insert Bars At Beginning
This plug-in inserts any number of bars at the beginning of the score, setting the time signature and key signature of the bars to be added.
The system text from the first measure is copied, deleted, and repasted to the new first bar to make your life easier.
In Sibelius you can insert bars at the end or in the middle, why not be able to add them to the beginning. If you do any serious engraving or composing, you probably won't want to go without this one.