Hi RK,
If same holiday calender is used for 3 locations and a new holiday needs to be added to this Hol Cal(applicable only for 1 of these 3 locations) then I suggest you to create a seperate Holiday calender for the location to which has this additional holiday.
Holiday calender 1 - Location 1 & 2
Holiday calender 2(with additional holiday) - Location 3.
Hope this helps!!!
Regards,
Hari