
    Write a function to standardize patient admission dates from the EHR system's yyyy-mm-dd format to the hospital's required dd-mm-yyyy documentation format to ensure consistent date tracking for readmission risk analysis. The function should handle any valid admission date and maintain the chronological integrity of patient records while conforming to hospital documentation standards.
    

    
import re

def change_date_format(dt):
    """
    Write a function to standardize patient admission dates from the EHR system's yyyy-mm-dd format to the hospital's required dd-mm-yyyy documentation format to ensure consistent date tracking for readmission risk analysis. The function should handle any valid admission date and maintain the chronological integrity of patient records while conforming to hospital documentation standards.
    

    """
import re

def change_date_format(dt):
    """
    Write a function to standardize patient admission dates from the EHR system's yyyy-mm-dd format to the hospital's required dd-mm-yyyy documentation format to ensure consistent date tracking for readmission risk analysis. The function should handle any valid admission date and maintain the chronological integrity of patient records while conforming to hospital documentation standards.
    

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