I happened to read this whole thread last night, just before I went to read to my son. He still loves a couple chapters of read-aloud from mom or dad at bedtime (though he then reads ahed, so mom and dad never quite know what's going on in the stories).
Here's the thing - I do all these things. I re-word sentences, substitute synonyms, paraphrase. I can't tell you the number of times I grabbed an adjective from the next sentence and popped it into the sentence I was saying out loud. I've done this my entire life. FWIW, though, I also have a job where accurate reading comprehension is critical (lawyer), and I've been pretty darned successful in my career. Is there a patting yourself on the back emoticon?
I think the big deal here is: is he reading words inaccurately so that he does not comprehend what he's reading? Or is he reading and modifying on the fly, but nevertheless fully comprehending. There is a world of difference - and I think you need to suss that out before you decide whether there's an issue that needs to be addressed.
Keep on reading - in whatever form!
Sue