Yes, Nintendo confirmed that changing the lithium battery pack inside your controller is OK, allowing fans to replace the battery pack at their own whim. It might seem a bit trivial, but it’s not often that this power is given to fans these days, since the introduction of lithium batteries.
There are advantages to replacing the battery pack. Lithium batteries can lose capacity over time, making your battery life slowly dwindle away until you’re charging it every single hour. If you can replace it, then there’s no fear of having to buy a brand new GamePad just for the convenience of not charging so often. This also opens up a market for third party battery packs which might hold more charge over a longer period of time.
Nintendo has already estimated that after roughly 500 charges, your battery pack will have deteriorated to 70% efficiency, so putting this power in the hands of the people is a positive step forward.