I think that burning all those "short threads" out of the pattern from the moment they were born even wouldn't have had the world warping effect that burning out Grendal's thread which spans THOUSANDS of years would. I think that is the larger part of the "warping effect" Although, that many in a localized area...

Also, I think that the whole warping them to free souls thing works. You can burn them back before any promises were made to the dark one, thus he can't grab them even if the window of time was good. Or maybe THAT is the window of time RJ was referencing.

I think they can be respun because the wheel doesn't come with the thread to start with. It comes from somewhere. That "somewhere" will produce it again.