There are many ways you could do backprop... if you want to probe the values straight from the middle of the grid, you could do that. You could poke new values right into the middle of things (by using configuration/random access mode), but everything else is going to pause while doing so. Or you could ripple in new weights along with data.

To me, this feels like starting from where Turing stood and inventing a new type of computer. The sky is the limit.