Is there a function to test if model number is viable?

[Sir Vendel]

I make some scripts altering PCs appearance, and customizing item appearances.
After using the SetCreatureBodyPart(CREATURE_PART_HEAD,x) part for, e.g. head for a creature, I would really like a function that could tell me (TRUE/FALSE) whether part x is a real model, or if my PC now is headless.
Is there anything like this already existing? Or could someone undertake to add the function to nwnx_funcs?
Similarily, upon using CopyItemAndModify() to, say set a shield appearance to 139, is there a function that could tell me whether #139 is a viable model, or if the shield just disappeared?