You can change the name of any file to longer than standard Mac defaults simply by doing so in the shared window. Limewire will truncate the name in its usual way.

If you want a file name you can recognize, then make an alias to the mp3 and place in your shared folder, then change the name of the alias in Limewire's shared window.

This may be a little extra work, but it has advantages: you can keep the original in your iTunes folder and it gives you more flexibility as to what files you share and when. Further, if by change you delete a shared folder in Limewire, all you have lost is a bunch of aliases.

Multiple aliases are quite helpful to those who download from you, esp. with larger video files that carry several names on the network.