the stuff listed here is a way to legaly field a genestealer cult army in games of 40k. i have also added some none-official extra rules for friendly games at home.

special ecuipment: chem-inhalers

skills and drills: hardened fighters

skills and drills: light infantry

the chem inhalers can be used to represent the hive-minds grip over the cult, the models don't really need to have chem ecuipment. hardened fighters provides it with a better WS, what else could genestealers need?. light infantry adds infiltrate, which fits very well.

what to represent as which units?

you could use the old genestealer cult models if you have access to them. or else you can convert imperial guard models into cultists, and Hybrids by combining genestealer parts (heads and arms) to them. but the list bellow guides you to see which Genestealer units that can be used as which Imperial guard units. note that this list is made with the existing cult models in mind.

the officer could be represented by a Genestealer patriach or broodlord model. only give the model CC upgrades like power sword or power fist. it can also be represented by a leader-hybrid.

the command squad consists of several models, most likely hardened hybrids that leads the cultists. use hybrid models.

-medic: the medic can be any hybrid but, either with stolen med-kit or, maybe some tyranid symbiotes that can give healing abilities

-Vox: the vox model can be represented using a genestealer, considering it gives strenght to the hive-link.or if not, a hybrid with vox and/or hive-node represented convertion

-banner: a hybrid with banner or hive icon, maybe even a pure genestealer to represent the purity of the tyranids and so works as banner.

-Officer: represent by a hybrid that stands out in some way, to represent a leader

-Comissar: could be a hybrid that stands out, or a genestealer to represent a tyranid-representant among the units to further enhance the morale

-sanctioned psychers: the only psycher in the army list and so should represent genestealer Magus

-Priests: should be a hybrid

they should be represented by hybrid models, and so should veteran sergeants among cultist squads

they should be represented by either the larger plastic hybrids, or by hybrids with some extra bulk or armour converted to them

the standard cultists that should be using the cultist models. each command squad to the units should be hybrids (see above).

could be either hybrids or cultist as crew.

this big guys need to be represented by bigger models. tyranid warriors is one option, but the ogryn behavior isn't really tyranid-ish. the best choice is to use the old models called Zoats. those where tyranid slaves and so could be in service of the genestealer cults.

you can use vehicles. if you want to model visible crew or pintle-mounted gun operators, use cultists as those are the more human ones, and should be more used to piloting vehicles. it can be cool though, on basilisks to use a hybrid to represent a slaver to get the cultist crew to work.

you can add 0-1 Genestealer broods from Codex: Tyranids. this occupies a Elites slot.

you can use 0-1 Broodlord and retinue from Codex: Tyranids as a HQ choice

you can induct Tyranid units to the cult. they will ocupy the same slots as in the codex. however you must have at least the standard recuirements from the cult list, HQ and two troops.note that you can't add monstrous creatures.

you can induct cult units to the tyranid swarm. the tyranid swarm must have all minimum recuirements on the force organisation chart. note that you Can't use vehicles in the tyranid army.