So, my players showed the same concern about the loss of the Void Born's "Charmed" trait. The Void Born player ended up getting over it, but I swapped out the talents for Void Born because they can be anything but "Unremarkable". Instead, I gave him Disturbing Appearance (a variant of Disturbing Voice) and Peer (Void Born). The loss of "Charmed" stopped being an issue after that.
I changed the Charactersitic Bonus given when you select your Specialty to a first, free Characteristic Advance in that characteristic. I think this will prevent PC's from having absurdly high stats in the late-game, since most games don't use an entirely random method of Characteristic Generation and it isn't uncommon to see a well-optimized psyker with 60+ WP. Of course, if you do use a random method, it might be best to keep it as a Characteristic Bonus.
On top of that, my players expressed a desire to have a choice of which Characteristic gains that free advance. I let them take that free advance in any Characteristic that they had an Aptitude for. Our Guardsman ended up taking his first free advance in Perception. Fine by me.
Guardsman thought that "Weapon Training (Las or SP, Heavy )" should be "Choose Two: Weapon Training (Las, SP, Heavy) by ruling that not all Guardsman would have proficiency with Heavy Weapons. I also swapped out the "Finesse" Aptitude for "Fieldcraft", since I find it bizarre that Guardsman aren't proficient with operating on the field of battle.
However, this is remedied for a Guardsman wanting to play a Sniper or any such variation of a Specialty by implementing your Characteristic Substitution system (I actually called it Variant Specialties, inviting players to come up with a name for their modified Specialty). Perhaps I'm less concerned with balance and more concerned with player customization, but I think this is a wonderful system. I'd actually come up with same exact one a few weeks back and found it hilarious that we had the same idea. My Guardsman ended up swapping Defense out for Offence, claiming that he was a Penal Legionare. Hey, it works for me.
I'm also tinkering with your Interrogator career at the moment.
Ah, I had been rather unhappy with the Void Born origin. Your changes make a lot of sense.
That change (free Advance instead of a free bonus) is clever! I quite like that.
Finesse was chosen for the large number of Ballistic Skill-related Talents out there that use Finesse as their secondary Aptitude, along with it being the Aptitude for Weapon Training talents. That said, Fieldcraft and Defence make for a pretty handy combination. I think I'll make that change!
The Interrogator is one I'm not happy with. He's definitely a WIP, as I struggle to define his role. Is he a social character? Is he a Jack Of All Trades? I can't decide, hence his lousy status.
Good to hear all of this, I hope the game goes well!