The reason most folks don't do huge water changes is that the tap water is often a little different from the tank water in regards to hardness, pH, & TDS. If you do large water changes often, your tank water is nearly identical to your tap water, so a couple of large water changes won't harm anything.
In your case, any water change is going to be adding water that is different from the tank, so you really have no choice. I would do several large, 50%+ water changes with about an hour in between. Adding chemicals to lower the pH might lower it for a short time, then it will rebound up. This is less likely to happen with water changes alone. Doing 50% daily could take a week or more to bring it back down, as two 50% water changes is the same as a 75% water change.