You need to flash your FS eu4.
But you need to flash a fake main in order to acces FS with Far Manager and apply customization. Look on download area for your FS and also CDA acording to your country.
Read carefuly tutorial about debranding, links here on page 3 I think.
Follow the tutorial : download the files and use the first fake main to get acces to FS with Far manager and SEFP plugin. Then final step write your main again.

@Eddie: "After unlocking I have flashed it back to ...."