Here are my ideas for using the Tyranid Codex for a Latd army.

Tyrant - Mutant Lord- large mutants which lead the hordes of of renengades and mutants through sheer fear and with minute mind powers - model represented by new FW Dp... armed with venom canon

Lictors - war Hounds - large dog like creatures bred by mutants to scout ahead of the force attacking units in packs - models to represent them, hounds of Xaphan.

Warriors- Spawn - the muatated creatures of chaos which are idolised by lesser beings, like men.

Genestealers - Mutants - Hordes of devloved humoids with the touch of chaos lingering in their flesh - models to represent them, VC Ghouls with gs conversions.

Gaunts - Heretics - the thousands of men that have turned to chaos - Models to represent them, Empire Flagellents with FW renegade militia weapons.

Zoathropes - Rengade Psykers- The Psykers which have been taken by chaos rabble from imprisonment by the imperium - models to represent them, FW rogue Psykers.

Carnifex - Great Spawn - the largest of the mutants after the Mutant lord, these are the shock creatures of Mutant horde, set onto the enemy in masses of mindless flesh.

what do you think, it's a tempting idea and i thought I'd share it with you.