Cool Edit will not lower quality. (That is, unless you re-save it in a lower quality format.) I've never used Reason so I don't know if it lowers quality or not. I would certainly hope not.
Something to consider is...mp3 is already a lower quality copy of the original recording. You would be better off starting with a wav file, which is higher quality, uncompressed data.
I would sample the MP3 and save the samples as .WAV files. Then any other processing you do on the samples won't effect the quality of them (until you mixdown and convert the song to MP3).
Although most editors will work with MP3 files as WAVs anyway when you import them into a project.