As noted, you should save the original recording.

I would also note that you should of course save a copy of the original mp3, or better, make a copy and do the correcting on it, since the digital version is likely to be more durable than the analog tape.

Just copying analog recordings can give differing results, and in some cases makes slight changes to the original, so they can "wear out." Common analog media, like tapes, also can just "die of old age." Analog records just aren't really "archival."

A copy of a digital record, on the other hand, should be an exact copy, and as long as the medium where it's recorded survives you can make an exact copy from it - often even if the first one is on a drive/disk that might be deteriorating.

And when making "corrections" it "just happens" sometimes that the best way to correct a correction that doesn't work out is to start over with a fresh copy from the original.

John