There are tag editting software packages. For example, metax and max will edit video and audio tags on the mac. Set the ratings, remove explicit, etc. It's really not that tricky, just requires software. MetaX is part of my dvd-ripping routine. Handbrake to MetaX to iTunes.
I'd bet Doug's apple scripts has something, too.
As to the "no external media", yah, it's a streaming device. You can use external media, it just has to be in itunes, and be attached to your computer, not to your tv.