No, it wasn't left open. Contractors that wished to make substitutions were supposed to provide cut sheets along with a request for the substitution to be approved. That was supposed to happen during bidding, but it didn't.
There is no way to know, but I suspect the difference in price is probably pretty minor. If I asked how much they saved, I'll bet the contractor would say "These were actually more expensive, but I like this supplier because blah blah blah..."
I think that's a pretty good idea, even though bidding is over. At least they would have to admit its a substitution, and maybe even sweat a little. And it would also be a minor pain to the contractor, which Charlie suggested.
On a side note, this contractor also
sent an entire catalog of electrical boxes as a submittal. No indication of what they are going to use, just sent a catalog.