I have no particular background in neurology -- my goal was an order-of-magnitude estimate for how much storage it would take to describe a brain accurately enough for simulation.

Accurate enough for simulation is a tricky term. It depends on the purpose of the simulation. If you just want to simulate what happens in a time window of 1 second you can ignore changes in myelin sheath thickness. But the resulting system isn't equivalent to a human brain and it's complicated to argue that it's conscious.

When it comes to long term learning neurons are capable of expressing genes as a result of neurotransmitters. We don't know the functions of all genes in the human genome.