If the pump has a variable frequency drive, yes it can be turned down. Think of a motor that can run faster or slower. If the pump isn't like that, then choking down the flow puts more strain on the pump (backpressure) and shortens it's life. How short? I can't say.
In simple terms, putting O2 into the water makes the iron precipitate out if the water would go into a pool and not have a fast flow to the pond. Sort of like a settling pool.
The more air (Oxygen) you can get into the well water, the better.
| 
