LIB Folder for arduino core file

Hello all,

I have a doubt ,i want to edit USB core library of arduino, but i want it to be modified only for that particular project. I know that private libraries should be in Lib folder in PIO. If i will add the changed USB core lib to the Lib folder will PIO use the one in the lib folder or it will take the lib from Arduino core. I read that lib folder has highest priority for LDF in PIO documentation but i am skecptic because its core file of arduino.

Thanks you all for your time

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