If you can update with changes on the fly, then you can propagate errors on the fly as well. There are likely some quite fatal corner cases that could be found the hard way.
It's a good thing we aren't using updated updated-on-the-fly computer systems for controlling powerplants, chemical refineries, trading on finacial markets or driving cars!
Knight Capital updated their your stock algorithms on the fly, instead of properly investigating the cause of failure[1], resulting in a loss of USD$460 Million after unwinding most of the trades with other firms.