If your CD or DVD is "Read-Writeable" or "RW" then yes you can add more files to the disk until it becomes full.
If you have a CD or DVD with just “R” on the label, you cannot erase the disk and you cannot add files to the disk after it has been finalized.
To remove files from a "RW" disk you need to ERASE the whole disk first which means all files stored on the disk are deleted.
See also -
Is the internet filtered?Information on the internet filtering in place on our PCs and wifi.