Coronation
Though the Palatines have emperors, the Senate in Atrans has historically been very powerful, and capable of restraining the emperor. The relationship has been such that unlike in many other monarchies, the emperor's heir's inheritance of the throne is not to be presumed. Indeed, Palatina has been known for at times long interregnums, where the Senate manages the affairs of the empire in lieu of an emperor, often by appointing a temporary dictator while the Senate searches for a suitable emperor from among their number.
History
The Palatines did not always have emperors, and indeed the Senate is the older instutition by far. The tradition of emperor arose out of the demands of the ever expanding empire, increasingly difficult to rule by committee from Atrans. While many senators were out leading the senatorial legions, the empire found itself needing to vest the powers of the executive in one person. However, the Palatines have always believed that the proper place of power is the senate, and thus the office of the emperor is conceived as a grant from the senate, rather than anything which exists by right.
In recent times, coronations have been more contentious, as the less established House Maursus has gained primacy. Some senators even believe that in the current state of the Palatine nation, an emperor is not necessary.
Execution
The first step of a coronation is for the prospective emperor to be nominated by one of the senators at a time when there is no reigning emperor. The emperor-to-be must win a vote in a senate, gaining the support of over half of the chamber. Once this is done, the coronee shall march to the Temple of Lavian with their supporters at dawn two days after the vote. There, the chief priest of Lavian shall offer sacrifice to bless the new emperor's reign. The emperor shall swear and oath to the gods, promising to uphold the Palatine people.
Once the emperor returns to the senate from the temple, they will enter a sitting of the senate, take the podium, and declare "The gods have accepted me!" Thereafter, the emperor can begin their work as the new ruler of the Palatine nation.
I like that there's a bit of a rumble that an emperor might no longer be necessary. Nice little touch.