Can't add files to bootable usb

I created a bootable Lubuntu USB using a Ubuntu 16 machine using the startup disk creator tool in Ubuntu. the disk is created well. than i need to add a file to the folder EFI/BOOT

I need to add there the 32 bit bootloader and try to use sudo cp bootia.efi /media/user/Lubuntu 16.10 amd64/EFI/BOOT/bootia32.efi and get the following error:

cp: cannot create regular file '/media/user/Lubuntu 16.10 amd64/EFI/BOOT/bootia32.efi': Read-only file system

Seems that the file system is read only, i changed the read only bit, as explained in the following link as explained here

And still get an error that says the drive is not writable. How can I make it writable?