I would.
Just add slow, mix well and recheck often; there's probably not much of a buffering capacity to the mixture, so the pH may swing harder/wider/farther than it would under more 'regular wine making conditions'.
I'd probably add 1/4 of what you think you'll need, then recheck, and add another 1/4; rinse/repeat until it's where you want it (~ 3.4 ish)