it shouldn't make a difference; certainly my odi switches between psg and ppc no problem (though I don't have hepts so I can't comment on that)
I'd forgotten that titans could carry PSGs, my next M2 is definately a titan!
I went code diving and I figured out how the game works out the amount of personnel that are available. One thing I discovered is the fact that all AI cap ships (not M6,Novas or TSs, strangely) will respawn with alternate weapon loadouts, which is a good reason to restart.
I haven't yet
(we don't just restart for patches and expansions now, we restart for scripts

)
anyway, how you know how much you wil get:
there's a 5% chance of you getting between 0 and all crew, a 10% chance of 0 to 20, or 0 to 5 crew otherwise. All will disappear in between 1 and 5 minutes. Which puts PPC shortages into perspective - yet it's a ludicrously good upgrade, so perhaps that's OK.
Idle crew - ones stockpiled on your own trading docks or extra ones on ships - disappear at between 1 and 50% every 15 minutes, at the same time as more transports are sent out.