Did the same thing on my Accord.
It had as OE, the little rinky dink 51 with about 400CCA.
When it got below 20 degrees F, it was hard to start.
So I ordered a 24 Gold on line and went in for them to install it.
The installer went nuts, stating that that was the wrong battery because the hold down wouldn't fit (however there was more than ample room for the 24.). He wanted to put another 51 in it. I refused.
I said "It will when I get done with it." I then grabbed a pliers off his little cart and bent the tab back on the hold down (like you did) that was holding the 51 in place, and gave it back to him. He balked but put it on and the battery held strong. Worst case scenario, I would have gone in the store and bought a universal battery hold-down and used that.
Hold down fit fine, and the car starts stronger, now that the battery is properly sized.
I was told (by a tech @ the dealer) that Honda switched to the 24 size battery on the Accords midyear during the '12 run because of complaints (not sure of the accuracy of that statement but it seems logical.)