As far as I've ever seen, no, there's no tool that can split a GBS or NSF into separate files. However, a few years back I got a tool off of Zophar.net that could log a song in an NSF to a separate NSF. However, this tool wasn't perfect (sometimes it was fuzzy, or had pops, or just sounded wrong), and frequently resulted in a file that was larger than the original NSF. And, because it used some method of logging, the song stopped playing after a certain amount of time (I don't remember what the length was). But, these files did play in NSF players, so the results did "work." Unfortunately, I don't remember the name of the tool, and I didn't know where to look on Zophar's current site to see if it's still there.
If that will accomplish what it is you're looking for, I might be able to see if I still have it on my PC, but don't get your hopes up. It was a good long time ago that I downloaded it. And no, I can't think of any tool that could do that for GBS files. Mouser X over and out.
You can also make .m3u files pointing at specific tracks within an NSF/GBS. VGMToolbox will create .m3us for GBS files, check the "Output additional .m3u per track" to get one .m3u per track in the file. If it is useful, I can add similar functionality for NSFs.
EDIT: The VGMToolbox created .m3u files are nezplug compliant and will only work with plugins that support that playlist format.
For NSF, you could convert to NSFE, copy and paste the file for the number of tracks it has, and then make each file have only one song in the playlist. So, if you don't care about a "true" split but rather want to navigate to tracks quickly, that would be the way to go. Well, that or M3Us (though those won't allow for advanced tagging).
by nensondubois at 10:26 PM EST on November 17, 2009
for NSFs was a tool at Zophar's domain (or at least there used to be but since the new staff sucks, everything useful is now gone) but alternatively, you can download it here http://www.neshq.com/nsf/ that can rip specific or the entire NSF in into individual NSFs but there is no support for games that have their sound engine where bankswitching is used.
Edit: There is no tool for individual track ripping for GBS files.
The tool that nensondubois is talking about is the same tool I was talking about. If you check the readme.txt, you'll see that it mentions a few problems that the ripper has, which are the ones I talked about (though, it doesn't mention that the NSF eventually stops playing. Maybe I remembered it wrong? Then again, I might have tried to play it for a ridiculous amount of time). So, yes, it "works" (as I said earlier), but I wouldn't necessarily say it works very well. But hey, give it a try, if that's what you want. Or, do as the other posts in this thread said, and use NEZplug+M3U playlists, or NotsoFatso+NSFe (NotsoFatso can "split" files via M3U playlists as well, but it uses a different method than NEZplug). Personally, I recommend NotsoFatso+NSFe, but that's because I like NSFe files. On my PC, I have NotsoFatso and NEZplug installed. NEZplug plays the NSFs, and NotsoFatso plays the NSFe files.
Anyway, hopefully at least one of these suggestions provides an answer close to the one you're looking for. Mouser X over and out.