This can stack with the +5 opinion modifier from being Born in the purple, and the +10 opinion modifier from rapidly accumulating 2000 prestige. Restoring Rome has the following effects: The Byzantine Empire must also be your primary title.
With Legacy of Rome expansion, it is possible, as Emperor of the Byzantine Empire, to restore the Roman Empire by controlling key duchies of the old empire. The Roman Empire is a titular Empire title. Duchies highlighted in yellow are required for the restoration.