If two or more candidates with identical first and last names file for the same office in a primary, general, or special election, the filing officer shall notify the candidates within five days after the nonincumbent filing deadline for that office and specify that the candidates' names will be differentiated on the ballot. Notification shall be made by any method specified in section 25-505.01. If an incumbent of that office is one of the notified candidates, the incumbent may choose a varying combination of first and middle names and initials by which to distinguish the candidate or to have the candidate's city of residence printed beside the candidate's name. If the incumbent does not make a choice within five days after notification or if none of the candidates are an incumbent of that office, the filing officer shall designate the names by which the candidates will be identified on the ballot. The filing officer shall use a varying combination of first and middle names and initials or include the city of residence of each candidate.