While it isn't possible to use Apple's iTunes software to transfer music to your shuffle from a second computer, without losing your current music, there are alternative transfer utilities taht are well suited to handle the job. The simple file structure of the iPod shuffle--compared to more advance iPods like the iTouch and iPhone--makes it easy for third party developers to create work arounds for transfer restrictions placed on your shuffle. With the help of a third party utility, you can safely set up your shuffle for music transfer from any computer.
Download a copy of Rebuild_db to facilitate the transfer of music from your computer to your iPod Shuffle. Rebuild_DB let's you store your music files into any folder on your shuffle that you choose, and you can even create your own. And after your songs are loaded onto your shuffle, Rebuild_DB configures your shuffle's database to make them recognizable by your MP3 player.
Use iShuffle to validate the files on your iPod shuffle. After creating a music folder and storing your files in it, all that is needed is to copy the iShuffle utility to your iPod. And after running the program, from your computer, iShuffle updates the "iTunesSD" file on your shuffle to include then newly transferred tracks to your iPod tracklist. And since the iShuffle utility is saved to your iPod, you can validate newly added files from any computer.
Use Gtkpod as an iTunes alternative with support for Mac and Linux operating systems. Gtkpod let's you transfer music, audiobooks, and podcasts to your shuffle. After storing your media in Gtkpod's "local database," all that's left to do is simply drag and drop your media directly to your iPod.