OK - First, adding acid actually lowers pH. The lower the pH value, the higher the percentage of free hydrogen ions (+ charges) in the liquid and the more "acidic" it is.
And yes, adding acids to the mead will definitely impact the flavor. As with any other fermented beverage, meads with too little sensible acidity taste "flabby," with no edge or bite. Adding some acid in that case can perk up the overall flavor profile. BUT CAUTION - I have come across very few meads that, IMO, would benefit from an addition of acid. Most traditional meads that I've tasted (along with virtually all the melomels that I've encountered) are already pretty well acid-balanced. The exceptions that I can think of are limited to very sweet meads (which can taste "cloying" without some additional acid bite to balance the sweetness), or those made using very alkaline water.
The best way to determine if acid additions would help your mead, is to try a few small experiments, where you add different amounts of acids (acidic fruit juice, acid blend, or tartaric or malic acid) to some test samples and taste them. I recommend that you never add acid to an unfermented must or to a mead that hasn't finished fermentation -- and that you never add any unless your taste tells you that it is necessary. You could easily add so much acid that you render the result undrinkable -- go carefully!
