Hi stefano conegian
Unfortunately the developer does not take your requirement into account in this demo.
The example demonstrates basic operation we can do with flash memory including writing string or characters into the memory and reading it back. The memory characteristic, reading and writing statues as well as the data are displayed over output terminal.
This demo write the string to the flash with write function.
len = write(flash_file, buffer, STRING_SIZE);
In your case you need to keep previous data, I think you can read data from flash and store it to buffer, and add new data to buffer, and then write the whole buffer to flash. It will be ok.
I hope it helps.
Thanks
Regards
Daniel