Once a CD-R is burned and finalized, you cannot add anything to it.
These are audio-CD's, correct? The only way to "tag" audio CD tracks is to add CDtext when you burn the CD. And even then, only certain CD-ROM's and a select few Sony CD players will be able to read the track info. However, at least they will play properly.
And in CDtext, basically all you can have written is the Artist, Album and Songtitles.
So, if you
really think it's worth it, you can rip the CD's to WAV files using a program such as
CDex, then burn those WAV files onto a new audio-CD, this time using a program such as
Nero - Burning ROM and adding the CDtext.