There are two different ways to edit .wma files. One way is to convert them to uncompressed format (like .wav files), work on them, and then export them to .wma or any other compressed format. That's called "transcoding". The other is to edit them without decompression, which limits the editing options but avoids any generation loss in going from the original to the final file.

I assume (but don't know for sure) that what Audacity does is transcoding. I am sure that's what Goldwave, a low-cost but not free wave editor, does with .wma files. In fact, Goldwave converts every format to an uncompressed one in its internal buffers.

I looked at a lot of web postings last year to try to find a .wma editor that worked without transcoding. There was a suggestion that the free Windows Movie Maker under XP would do the job, but I found that program very slow, and it wouldn't export .wma bit rates as high as I was downloading from the BBC, so there would be a loss of quality.

I've recently bookmarked a web site for another product that claims to be able to handle .wma without transcoding: SolveigMM Video Splitter, Version 3. It was last updated in August 2012, so it's actively being maintained. It costs €39.95, and a trial version can be downloaded, but I haven't yet had the time to try it myself.