One of its scripts disables the checkbox unless a specific faction pick has been added to the character in the background tab (in addition to the deity pick for Iomedae).
Code:
if (hero.childlives[facGloryRe] * hero.childlives[deiIomedae] = 0) then
perform assign[Helper.ChgDisab1]
done
endif
I'm not sure which source includes the Glorious Reclamation faction (facGloryRe) though, since I don't have it as an available choice.