
    Write a function that reformats patient admission dates from the hospital's legacy system format (yyyy-mm-dd) to the new standardized medical record format (dd-mm-yyyy) to ensure consistent documentation across all patient histories. The function must handle all valid admission dates while maintaining data integrity for critical medical records.
    

    
import re

def change_date_format(dt):
    """
    Write a function that reformats patient admission dates from the hospital's legacy system format (yyyy-mm-dd) to the new standardized medical record format (dd-mm-yyyy) to ensure consistent documentation across all patient histories. The function must handle all valid admission dates while maintaining data integrity for critical medical records.
    

    """
import re

def change_date_format(dt):
    """
    Write a function that reformats patient admission dates from the hospital's legacy system format (yyyy-mm-dd) to the new standardized medical record format (dd-mm-yyyy) to ensure consistent documentation across all patient histories. The function must handle all valid admission dates while maintaining data integrity for critical medical records.
    

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