If you do "Get Info…" on the song, under the "Details" tab you can manually change the track number.
For example, you can change it from 2317 of 15000 to 8 of 15000. That should reposition it, if not physically, at least while playing.
Don't those track numbers relate to a song's position on the medium on which it's included, rather than in iTunes, itself?
As far as I've ever seen, iTunes doesn't attach track numbers to songs on its own.
