This is certainly a conceptual idea I like and would support.
My guess is that food is generally scripted and the Manna bread is also scripted and there'd be a lot of coding nightmares. But, that's just an informal hunch.
Each race does have several unique types of manna bread they can create, though, if you weren't aware of that. It uses the SUMMON verb after 203 is prepared. There's a section for Bread Types here:
http://www.krakiipedia.org/wiki/203My guess is that your best bet is to expand the options for SUMMON to add even more flavor to the spell.
You know, because
some of the existing options give a poor connotation, such as the halfling "EAT MY DUMP" or the sylvan "EAT MY SEED" possibilities...
>An officer of the Sorcerer Guild arrives and glances around. "Ah, there you are, Vathon!" he says in a slightly agitated tone. "I have come to formally declare that your membership privileges have been revoked."
