OK thanks everybody.
Just a few notes.....
I found it strange that the Genre box worked differently from the Title, Artist, Album, Year, Track & Comment boxes, but I accept Florians view on the "why".
I have named my new box "Used Genres". I'd be happy with this box just being a none editable alphabetical listing with or without the " & " parts showing. May be not showing those two first parts would indicate that this box is a none editable list. Which would give me a shorter list than the current box. It will also list those typo's & none standard types which the current box does not do.
I know currently my new box is an editable box as it overrides and disables the original Genre box.
I could sort via Genre, but some people load their whole collection, something I've not been able to do for sometime until now, and this could take some time.
We can already add none standard genre types. And these are lumped together with the standard genres. How well does that sit with the ID3 standard mentioned by ohrenkino.
Oh one more thought...
If this is to be implemented, may be an option to make it an editable box or just a list when creating the new box via the options route. Or is that to confusing or difficult to learn for most people out there.