I had these tags in my file:
MEDIAJUKEBOX:TOOLNAME=Media Jukebox
MEDIAJUKEBOX:TOOLVERSION=9.0.63
MEDIAJUKEBOX:TOOLNAME=Media Jukebox
MEDIAJUKEBOX:TOOLVERSION=9.0.63
MEDIAJUKEBOX:REPLAY GAIN=-3.10661
MEDIAJUKEBOX:PEAK LEVEL=0.54248
MEDIAJUKEBOX:BPM=101
MEDIAJUKEBOX:INTENSITY=2
MEDIAJUKEBOX:TOOLNAME=Media Jukebox
MEDIAJUKEBOX:TOOLVERSION=9.0.63
MEDIAJUKEBOX:MEDIASOURCE=emusic
MEDIAJUKEBOX:REPLAY GAIN=-3.10661
MEDIAJUKEBOX:PEAK LEVEL=0.54248
ARTIST=Amelinha
TRACKNUMBER=5
MEDIAJUKEBOX:BPM=101
ALBUM=20 Super Sucessos
TITLE=Mulher Nova, Bonita E Carinhosa Faz O Homem Gemer Sem Sentir Dor
MEDIAJUKEBOX:INTENSITY=2
then I modified mediasource tag and I got:
MEDIAJUKEBOX:TOOLNAME=Media Jukebox
MEDIAJUKEBOX:TOOLVERSION=9.0.63
MEDIAJUKEBOX:TOOLNAME=Media Jukebox
MEDIAJUKEBOX:TOOLVERSION=9.0.63
MEDIAJUKEBOX:REPLAY GAIN=-3.10661
MEDIAJUKEBOX:PEAK LEVEL=0.54248
MEDIAJUKEBOX:BPM=101
MEDIAJUKEBOX:INTENSITY=2
MEDIAJUKEBOX:TOOLNAME=Media Jukebox
MEDIAJUKEBOX:TOOLVERSION=9.0.63
MEDIAJUKEBOX:MEDIASOURCE=emusic
MEDIAJUKEBOX:REPLAY GAIN=-3.10661
MEDIAJUKEBOX:PEAK LEVEL=0.54248
MEDIAJUKEBOX:BPM=101
MEDIAJUKEBOX:INTENSITY=2
MEDIAJUKEBOX:TOOLNAME=Media Jukebox
MEDIAJUKEBOX:TOOLVERSION=9.0.63
MEDIAJUKEBOX:MEDIASOURCE=emusic1
MEDIAJUKEBOX:REPLAY GAIN=-3.10661
MEDIAJUKEBOX:PEAK LEVEL=0.54248
ARTIST=Amelinha
TRACKNUMBER=5
MEDIAJUKEBOX:BPM=101
ALBUM=20 Super Sucessos
TITLE=Mulher Nova, Bonita E Carinhosa Faz O Homem Gemer Sem Sentir Dor
MEDIAJUKEBOX:INTENSITY=2
MJ duplicates fields at each modification.