In variants with a vampire race, slow digestion should not affect their nutrition clock, in order to prevent them from using it to practically ignore the hunger mechanics as soon as they find a ring.

This could be flavorfully justified as them being undead and therefore not having a digestion process to slow down.

If you would get no benefit from using Elbereth because you are a vampire or otherwise evil, you should be prevented from engraving it.

When polyformed into a vampire, or when playing as a vampire in variants that implement that: Engraving on the ground in a scrawl of blood should expend nutrition proportional to the number of characters engraved, probably just 1 nutrition point per character.