If you want to change the default product installation to ZFS files, you can do it in the CSM Gui, Settings tab, System Settings, Software Installation are these options:
SIS Base Install - File System
- Product Specific File System:
- Hierarchical File System (HFS):
- z/OS Distributed File Service zSeries File System (zFS): <===
Do not forget to click on the "Apply" button at the very bottom of the screen to take the modification into account.