Because this is all tied to religious/magical significance the way I would probably approach this is to define more fully what is an honourable burial and reverse its symbolism.
The first thing that springs to my mind is Ursula Le Guin's 2nd Earthsea book "The Tombs of Atuan". If you haven't already read it (& depending on how much time you want to spend) this is a truly excellent depiction of the worship of a dark power of the earth that's stifling and oppressive.
I can imagine the culture you sketched decreeing a dishonourable execution to involve being buried alive in an imprisoning sarcophagus, wrapped with winding sheets of lead (i.e. totally immobilised) to emphasise total powerlessness. The eyes are left uncovered to add to the terror. Inscribed on the lead are hieroglyphs reciting:
- spells of impotence to nullify the victims magical power
- wards to prevent their rescue or location by magical means (i.e. from allies)
- passages from religious texts depicting the tortures that await them in the afterlife
- a list of their transgressions
- the curse falling on any who recite their name or deeds in the world of the living.
Maybe they could then be put on a funeral barge and floated down a subterranean river (i.e. a real-world River Styx) with carved stone banks. Hideous carrion-eating monsters and ghouls could inhabit the depths of this river.
In opposition to this, honourable burial uses motifs of raptors (phoenixes, or giant vultures or "sun birds" who carry souls of the dead to the sun), and the metals gold, bronze and copper (the metal of the sun and light and fire). This lets you use cool metal death masks and pectorals and armbands and stuff.
After cremation, the honourable dead have a life-sized clay or ceramic double of their body (i.e. baked in a kiln - more fire symbolism about passage form life to death) that is then buried on a seat / thrones in a tomb-niches in the side of of a pyramid. The niche faces outward with a slit for their eyes so they can watch out over / guard the lands of the living. The most honourable spots are that get the most sun. Each face (N,S,E,W) has its own mystical significance. Rulers are buried at the apex of the pyramid, then nobles or great heroes, and so on down to the deserving poor on the lowest level. Criminals are below the earth. So death is a handy tool for reinforcing the social order. This would work best for a culture that was:
- very hierarchical & ritualistic
- very focussed on the past & on your place in the afterlife
- a place where the living are constantly reminded of, and in the presence of, their dead ancestors.