Most such MP3 CD/DVD players don't read rockridge extensions. But they use the filename (and its suffix) to identify the file. So, if you have MP3s with short name (<= 30 characters), the suffix will be valid, and the CD player will correctly identify it as MP3. My solution looked like this:
Shell-Script ISO30:
.key TO/A,FILES/M
.bra {
.ket }
Echo >T:ISO30 "FailAt 21"
List ALL DIRS {FILES} LFORMAT "MakeDir *"{TO}%p%n*"" >>T:ISO30
List ALL FILES {FILES} LFORMAT "Copy *"%p%n*" *"{TO}%p%.26m.%e*" CLONE" >>T:ISO30
Execute T:ISO30
Delete >NIL: T:ISO30
This will copy the given files to a new directory, automatically truncating the filenames to max. 30 chars to conform with Level 2. I've also written a program to remove blanks etc from the filename, called PackFilename, it is available on request.