
    Write a function to convert emergency room admission timestamps from the hospital's electronic health record system format (yyyy-mm-dd) to the standardized reporting format (dd-mm-yyyy) required for patient tracking and resource allocation analysis. The function should handle valid dates within the hospital's operational timeline and maintain the integrity of admission records for accurate wait time predictions.
    

    
import re

def change_date_format(dt):
    """
    Write a function to convert emergency room admission timestamps from the hospital's electronic health record system format (yyyy-mm-dd) to the standardized reporting format (dd-mm-yyyy) required for patient tracking and resource allocation analysis. The function should handle valid dates within the hospital's operational timeline and maintain the integrity of admission records for accurate wait time predictions.
    

    """
import re

def change_date_format(dt):
    """
    Write a function to convert emergency room admission timestamps from the hospital's electronic health record system format (yyyy-mm-dd) to the standardized reporting format (dd-mm-yyyy) required for patient tracking and resource allocation analysis. The function should handle valid dates within the hospital's operational timeline and maintain the integrity of admission records for accurate wait time predictions.
    

    """
    return re.sub('(\\d{4})-(\\d{1,2})-(\\d{1,2})', '\\3-\\2-\\1', dt)