Hi Giri,
If I understood your query correctly, client wants to extend the additional public holiday of year 2015 to year 2014 also.
Extending it to 2014 and generating WSR will flag the particular date as public holiday.
However, it will not undo any quota which got deducted for that particular date in 2014.
You will have to resave the leaves for that period to ensure that absence quota doesn't get deducted for the given date.
It will trigger retro time evaluation and payroll run and system will do the recalculation.
Thanks and regards,
Vivek