[Richard Crowley]

"Albie" wrote ...
"Richard Crowley" wrote:
"Andrej Kluge" wrote ...
Albie wrote:
And I just have downloaded and used a program called "Audacity
1.2.6" in the event you want to go the hard route. This editor
would permit of channel-swapping, inter alia

On MP3 files? Without re-encoding?

No. Seems unlikely that there are ANY applications that can manipulate
MP3 without decoding and re-encoding. Same problem in the video
world with most flavors of MPEG.

Au contraire! I just did it. With Audacity, one loads an MP3 file,
edits same and then "Exports" it back to Either an MP3 file or a WAV
file! It probably does silently convert to RAW in order to edit, but
the user has no inkling of it.

NO, You DECODED the MP3 to WAV (or its internal equivalent) .
You may not have known that you did that because the application
did it automatically (and surreptitiously) behind the scenes. Then,
you re-encoded it back to MP3 (perhaps automatically without being
asked). But this is exactly what the OP was asking to NOT do.