Hi Smitha,
If the project is already go live, then there are some pointers to consider before changing the calendar.
Firstly, it is required to take a backup of the planning area.
While extracting from Planning area, create a transformation so that the data is extracted based on the new calendar so that you can re load based on the same.
Secondly, you have to de-initialize the planning area to change the SBP and then once you re-initialize the planning area, load the data from backup cube to the active planning area
Thirdly, check all objects of process chains and macros for the horizon as per the new SBP and adjust accordingly.
Regards
JB