I thought the Society was able to do this because they already had programs in the various Warship HPG programs, and access to the warrior caste mitochondrial DNA? Did they have something like this set up for the WoB also?
No. Even if the Society was faintly aware of the Jihad and Toasters, they would have no reason to believe that the Toasters are coming for the Homeworlds. (Maybe if the Society took over the Homeworlds during the WoR and erected a much better intelligence operation than the Clan Watch some decades later. But not during the WoR/Jihad.)
That said, I think we could handwave two things if the Society knew the Toasters were coming for the Homeworlds:
1) With limited exceptions, Clan and Toaster warships are both old SLDF models. Presumably there is some old, core SLDF operating system common to both that the Society could attack with computer viruses.
2) The Society created viruses that could wipe out trueborn individuals, blood heritages, and entire warrior phenotypes. Most clanners, including Society members and other civvies, probably have some trueborn DNA after a couple centuries of warrior test-downs into and reproduction with lower castes. Presumably the Society could create DNA-targeted viruses that leave anyone with a certain percentage of trueborn/warrior phenotype DNA alone (i.e., most or nearly all Clanners) but target those without that DNA (i.e., nearly all Spheroids).
And if they fought, it would be Mech force vs Mech force,
Actually, both forces made heavy use of combined arms, so I think we'd see lots of tankers, infantry, etc. too.
As for Erinyes vs Erinyes, well, there is something about throwing the first stone that comes to mind.
Because there were only one or two of these ships, they're really only good for cleanup in the Homeworlds. The Blakies would want to use their Q-ships to launch lots of nukes against the Homeworlds first. The Toaster warships, Erinyes, and/or Shadow Divisions are only large enough in number (especially after the Jihad) for escorting the nukes and eliminating weakened survivors.
But as the Regulans have shown, you can make a lot of nuke warheads and convert a lot of Mules to deliver them in fairly short order.