Use a discarded GW idea for emissary specialist. (ZOATS)
Before a planetary invasion, a group of emissaries arrives on a planet to negotiate surrender with its leadership. These aliens are humanoid, possibly religious zealots who worship the harvesters. They basically arrive, threaten the worst. Attempt to negotiate a peaceful surrender and the relinquishing of 2/3 planetary population, resources, whatever it is the harvesters come for. They send in the emissaries because they'd prefer to take planetary territory or resources without war or risk of casualty, so they send the Harbringers in to basically threaten world leadership into allowing the Harvesters to come, take what they want, and either build a hidden base close to the planets core (they love heat) or take more than what they came for and move on. Because honestly, who wants a war? Especially when you can get what you want without losing a single life on your side. Imagine too that these Harbringers have occasionally negotiated trade and alliances with the more warlike species in our galaxy. It is rumored that even Earth has dealt with trade of technology for population since the early 1940s, all thanks to negotiations of a Harbringer and Human leadership. A deal like this rarely ends wel for either side at the table. But the Harvesters are not beneath making deals or allies. And for this they send in a Harbringer with a quick wit and silver tongue.
These "Harbringers" can proxy genestealer cults, and space related games. Give them teckie space suits. Possibly torn and worn, to proxie as zombies, post apocaliptic. Etc. So many uses for them. Please give them a few head options ( plastic prints of your alien heads would do)
I would love to use them for Stargrave. Look to modern and vintage space suits for inspiration. Hopefully a couple of varying torsos.