Authors CurseForge

Theoretically yes. In practice, might be a lot harder. You'd need the spell IDs for all the food that gives Well Fed, possibly all the spell IDs for the other food that give various stats. I say this because looking up "well fed" on Wowhead returns a great many results for buffs.

Then securely hook UnitAura to check for the buffs; once active, hide the icon, then replace with one of your choosing, then show the new icon. You may be able to do this without secure hooks, but since auras are ever-changing, if only by time left, I figure that to be the safest route.

Quote from Seerah

But if you just want to change the generic cheese icon to a different generic icon (that would display for all well-fed buffs), this is MUCH easier. You need only do a manual texture override in the Interface folder.

I did think of that, but was concerned the cheese icon might be used for things other than the Well Fed buff. Still, you are correct that it would be much easier to override.