Yes. As long as the medium is still open and with enough space. HOWEVER, I must add that a .iso file is a disk image and it will probably try to copy itself unto specific parts of the disk (i.e. if it's bootable, it will try to write to the boot sector). This is not a problem if you have a re-writable medium, but since you don't, try the following to avoid any problems.
First you mount the .iso file to the cdrom device. Let's call the file "my2Gb.iso".
sudo mount -o loop my2Gb.iso /dev/cdrom
Optional: If you are uncomfortable or unsure about the cdrom, then make a directory and mount my2Gb.iso to it.
sudo mount -o loop my2Gb.iso /home/USERNAME/myiso
Then insert your medium (DVD), launch whichever application you use to burn stuff (k3b, brasero).
Locate the files, add them, and let it burn.