Unfortunatly not. Switch currently supports conversion to the following file formats:
.WAV
.MP3
.AU
.AIFF
.GSM
.VOX
.RAW
.OGG (Switch Plus version only)
.AAC (Switch Plus version only)
.M4A (Switch Plus version only)
.FLAC (Switch Plus version only)
But I can recommend you "Windows Media Encoder 9 Series". It will convert your mp3 file into wma file. See the link below:
www.microsoft.com/windows/windowsmedia/9series/encoder/default.aspx
Good luck 