First you gotta download a font you like, but they already have to be in "Helvetica/Helvetica Bold". Now, make a copy of both of those fonts and rename them "HelveticaNeue/HelveticaNeueBold." Then, go to System/Library/Fonts/Cache in WSCP or whatever SSH method you use, but before you drag and drop the font you want to change, copy these files as backups, "HelveticaNue/HelveticaNueBold," so when you want to change back to default, you'll always have 'em again. Now drag and drop the fonts you renamed to that same folder you got your backups from and after that, respring your device and you should see your music font changed. If you need more help, let me know.