How to write the data dynamically through USB

Hello friends,
 
I am working on PIC18F26J50. I am using its USB features for my application using 'MSD internal flash' USB code provided by microchip's  MLA. Till now USB interfacing is done and through this code I am able to detect my device as mass storage device on PC showing flash size upto 48KB right now.
 
Currently, when I am connecting my device to PC, I am able to see a .txt file in which default 'Data' is written. This is because of following content present in files.c of MLA project folder.
 
     #if (DRV_FILEIO_INTERNAL_FLASH_CONFIG_DRIVE_CAPACITY>0)
     const uint8_t PARTITION_ATTRIBUTES(SLACK0_ADDRESS) slack0[FILEIO_CONFIG_MEDIA_SECTOR_SIZE] FILE_DATA_ADDR_TAG =
          {
               'D','a','t','a'
          };
     #endif
 
Now my question is :  How to write the data dynamically instead of writing 'D','A','T','A' as default in the code? I found there are few functions like
1.  uint8_t FILEIO_InternalFlash_SectorWrite(void* config, uint32_t sector_addr, uint8_t* buffer, uint8_t allowWriteToZero) from internal_flash.c
2. size_t FILEIO_Write (const void * buffer, size_t size, size_t count, FILEIO_OBJECT * handle); from fileio.h
 
Are those functions useful? If yes, then how to use them? I can not find their function calls in the code.
 
Thank you!