Use these steps to change billing type for a WBS Element.
Role ZSBM =>Miscellaneous => Change Project
At the Command Line, enter: /nCJ02
WBS element (7-digit WBS element)
The "Change project: WBS Element overview" screen displays; the Basic Data tab is open.
Result: The Change Project: WBS element screen displays. The Billing Form field is in the middle column near the bottom of the screen, as shown below.