Thanks for the idea, Matt. I looked through the list of ElementTypes that can be set this way and I guess that PipeType is not the appropriate one for setting the current SystemType. But you got the principle right.
Literally I want to change the SystemType like choosing it from the dropdown list in attachment picture but via API. Or in other words is there a way to appoint the SystemType for pipe being created during its creation or right before it but not afterwards?