Heretic Plague
True to our name, we do in fact have the Microbe Division, made of up a hundred trillion crack microbe spec-ops teams, ready and willing to force anyone who ingests them to serve the Hive-Plague. To start simply, we have designed a modification to a single Genestealer, which secretes a compound containing a virus based on the Genestealer's DNA-injection system (That's what viruses DO, after all), which is, at present, only waterborne. This allows us to infect various numbers of people and gain immense numbers of recruits, very quickly, should the need present itself.
Greater Plaguemind (Does this have to be a Grand Design? I hope not)
A gradual adaptation to our Patriarch, focusing our hive mind on him and his will, allowing our pure-form units greater adaptability as the Patriarch changes their (Still beast-like and simplistic) orders as necessary. Not only does it tighten the Patriarch's control, but it also makes our hivemind stronger, binding our units together more than before, allowing for great levels of coordination against the machine-armed foe.
Alright, I'm going to suggest these again.
We're supposedly going to be suffering for manpower. Let's overcome that shortage before it even becomes an issue. Also, the Patriarch redesign is going to make our Purestrains much, MUCH more intelligent and capable against hostile forces.