Hello Rishi,
Planning calendar not override the factory calendar.Planning calendar work base on factory calendar days setting
But you can use the planning calculation rule to fulfill your requirement.
Set the calculation rule as "Do not Displace" and create the planning calendar with Saturday or Sunday and assign to Material master with lot size PK and check the result.
For more detail check the below document.
Planning Calendar Calculation Rule detail information
Regards
Umesh Mali