The question is whether that caramelization will continue on previously cooked bread.
What happens is that the higher moisture combines with sugars on the dough surfrace, forming an even layer, which then caramelizes to form the crust.
Once cooking is complete, and there is no longer any yeast or enzyme activity, does sugar still migrate to the surface? I think not. Nor do I believe there is enough on the surface, given the reheating times and temperatures, to cause further caramelization.
The problem, as I see it, isn't caramelization. It's simply drying. It's a matter of relative humidity. Unless the humidity inside the oven is at its highest possible level, additional moisture will be drawn out of the food. And I don't believe it's possible to achieve 100% relative humidity in a home oven. Certainly not on a sustained level.