Hi, i’ve made this using the get and set ParameterByName, with a little retouching you could get it to work in dynamo player to make it easier (like selecting one on the model, getting its family type and changing all of the rebars from that family type).
But as i was going to upload this i saw that the “B” Parameter you have is a read-only parameter.
I recommend you see this post and see if it helps a bit more