Function replace 

pub fn replace(
    engine: &mut EngineState,
    store: &dyn ModelStore,
    component_ids: &[String],
    source: &ReplaceSource,
) -> Result<String, String>

Replace the part shown by component_ids with source. One undo step; the mates’ report lands with the run (EngineState::replace_report). Returns the new parts-library entry name.