I have a Excel name "CCP_MARGIN_2017-09-11_risk_cpm_stg.xlsx" in C drive. I am reading it and using

CCP_MARGIN_2017-09-12_risk_cpm_stg.xlsx

You have a string and one part of this string changes dynamically, right? 

One way is to create a method which will return appropriate date:

def get_file_name(date_):
    return "CCP_MARGIN_{}_risk_cpm_stg.xlsx".format(date_)

Now if you call get_file_name("2017-09-13"), it returns: CCP_MARGIN_2017-09-13_risk_cpm_stg.xlsx

You can hardcode the date argument or make it more flexible using Python's datetime library.

For example you can set today's date:

from datetime import date

get_file_name(date.today())