CDs cannot allow the modification of files. CD-RW and CD-R are not the same thing. A CD-RW would allow you to erase and reburn, but you still cannot update files. Once the file is on the CD, that's it, the order of 0s and 1s cannot be changed. It is a ROM - Read Only Memory.
A floppy is of type RAM - Random Access Memory, which means the data can be manipulated and changed in real time.
You cannot uncheck the read-only, because the files must be read only.