Adding acid before end of fermentation?

Well for one, you should forget the idea of stopping a moving fermentation. It can/has been done. But it isn't at all reliable. You should pick an ABC. Use the appropriate amount of honey. Run it dry. Stabilize it. ANd then add your adjuncts. People have listened to bad advice for years about pH and what the lower level is. I have never had a single stall at, or above 3.0 in the 250 -300 gallons I have made.

Well So. If the pH goes too low it will make the yeast start making off flavors or just shut down completely. So that's why we suggest to add acid after it's been stabilized at least. Better yet if you wait to start adding adjuncts until it's gotten at least some clarity. Until you get a better handle on things. Some strains are more prone to make H2S than others. So every batch is different. However. I sometimes will pick a "less H2S" strain if I know a certain batch is already going to be prone to H2S. Anything apple immediately comes to mind.

For future reference, for reference of other newbees and for possible discussion:
"Citric acid added to a must before fermentation will largely be lost during fermentation. Thus, it is best to add it after all signs of fermentation have disappeared. Malic acid can be added anytime, but it too has a potential disadvantage. Malic acid buffers to a fairly high pH, so it should not be used if the intent is to increase acidity and / or lower the pH. In the latter case, tartaric acid is the additive of choice."
http://winemaking.jackkeller.net/acid.asp

So adding citric acid during a ferment is bad since much of it might be lost during the ferment anyway. You'd just be giving your yeast a hard time for no good reason. Since this was added towards the end of ferment it should be ok. Btw lemons have some sugar in them so this might extend the ferment just a little. Shouldn't have much effect here but it's possible that a ferment picks back up if you add lemons to secondary before stabilizing.

EDIT: It seems citric acid could increase or decrease during ferment depending on yeast strain according to Medsen Fey in this thread here:
http://www.gotmead.com/forum/showthread.php/20366-Acid-Metabolism-During-Fermentation

Medsen was a well knowledged contributor back in the day. one of the best we've had so that post's credibility is rather high. Wish I had more info on this subject. Anyway, unless reduction of citric is rare don't add citric acid before fermentation just in case the strain you use happens to metabolize citric