When reading about the late malt addition technique I read that you would get better hop efficiency with the late addition, so you should reduce the hops accordingly. I read this on the Midwest Supplies site, but was also told by Midwest Supplies live chat that I probably wouldn't notice much of a difference between adding the extract early or late. Whether or not this is true I don't know as I've only done two batches. As much as I enjoy the hops I wonder if overhopping is even possible.
No, you will NOT have any problem with using the recipe as written and adding the extract late. It used to be thought that wort gravity affected hops utilization, but that has been disproven.
One of the things to consider is that IPAs are hard to make as it is as a partial boil, to get enough bittering. The reason is this- there is a limit to the amount of hops oils that can isomerize in wort before being saturated. That is believed by most brewing gurus to be +/- 100 IBUs. That's a lot, so that's not a problem.
But say you are boiling 2.5 gallons of wort in a small pot. That means that the absolute maximum that wort can have is 100 IBUs (and most likely less). So, if you had 2.5 gallons of 100 IBU wort, and added 2.5 gallons of water (0 IBUs), that means that the maximum you'd get is 50 IBUs anyway, in a best-case scenario. In other words, you almost can not get enough IBUs for an IPA anyway in a partial boil so don't worry about reducing any hops!
IBU calculators are helpful, but not 100% accurate. Even a beer like Pliny the Elder that calculates to something like 250 IBUs has been tested, and it's more like 80 IBUs in reality!
When adding the extract late, it keeps the wort from tasting "caramelized" and darkening, improving the color and taste of the beer and making it more like the all-grain equivalent. Adding the extract at the end of the boil helps have a less "cooked extract" taste in the beer. It doesn't impact hops utilization in any meaningful way.