I would only adjust with tartaric acid, and not an “acid blend” that contains either malic or citric acids. Both of the latter can be fermented by organisms in the bottle. On the other hand, tartaric acid will stay put after you adjust it. Wine is especially rife with bacteria that will very happily eat malic acid, spitting out carbon dioxide gas, possibly-offensive off-odors (like diacetyl) and even possibly clouding up your wine with turbidity. Not fun.
Bacteria can metabolize citric acid into acetic acid and diacetyl, which is why I don’t recommend its use as a finishing acid either. The big downside to adjusting a wine’s acidity right before bottling, especially with tartaric, which can taste a little “harsh,” is that the acid just won’t have time to integrate in the bottle before you may want to drink it.
My longtime readers will know that I always advocate adding anything to your wine (if you are going to add anything to it at all) as early as possible in the wine’s life in order to give the elements the most amount of time to find themselves and make all the little chemical combinations (and possible instabilities) they’re going to make. That way, when it comes time to bottle, you have less chance of being surprised with a case of tartrate instability (crystals precipitating to the bottom of your bottles) or something even more unsavory, like a malic acid refermentation!
