Also what if a word they pick is also the name of an item? This would break the work they modified.

An example works for both: "Grill" do they mean to cook or to interrogate? And what if it is a grill as in the item to cook with?

And as for changing the spelling of words, well what if it becomes another word? Or maybe it gets changed into a name used in the book - this would cause confusion. And what about people learning the wrong spelling for words?

Of course there is also the issue of possibly violating the authors copyright by changing the work in question.