No one objected, so apparently it won't ruin the mod, at least not for any of us who check this site more than once a week.
Not sure Tchorak ships are actually Tier 4, more like 3.5. They can be beat by a number of different fleet builds that would be wrecked by the Kawangi. Just a reality check: You're aware that there's two versions of every Tchorak ship, right? So the Vent Mother and the VentMother do not have the same stats. Which one you're actually fighting really effects the difficulty of the battle.
Personally, I'd be a little hesitant to remove the weapon invulnerability, as it's one of the features that makes the tchorak unique. (The same could be said for the regeneration, but you've moved that to Ravians, where it makes more sense anyway.) An alternate possibility that would keep some of the unique feel, would be to keep the invulnerable systems (or reduce them to a system damage multiplier of .25 or so) and then just reduce the Hull (hit point) values a bit to bring them down in power. Or, just do that to the harder version of them.
Just a thought. As I said, changing these details won't ruin the mod for me.