Welcome to The World of CD-i!

You might be talking about using a CD-RW to burn you ISOs and then re-use them.

If I understand, you want to erase CD-RW discs and then make backups of your original discs.

Yes you can, but still not recommend. A CD-R is the best, but please keep in mind the CD-i players CD drives are single (x1) speed, that means they are very sensitive to any problem. As a CD-RW can be burn many times, the finish to lost quality, and they also need to be burned at the lowest speed as possible. I recommend a x4 if possible.

Please take a look at our PDF burning guide, available in the Downloads section to help you make it right.

CD-i Backup Guide

Quote from mycdi on 28/01/2021, 20:27

Can you erase, record over or add data to store bought (original) CD-i discs?

What format were these in (e.g CD-RW?).

No. Original discs (no matter if CD Audio or CD-i) from the factory cannot be erased or overwritten.
See Compact Disc manufacturing - Wikipedia