Development tools for Zephyr on STM32Workbench for Zephyr: VS Code extension to set up, build, flash and debug Zephyr applications on STM32.Devicetree manager: browse, edit and visualize Zephyr devicetree, STM32CubeMX-like for Zephyr.
I think it is better to generate a new project from CubeMX. I don't think you can change the MCU from the ioc file because there are compilation flags / or code that might change.