if you have a custom field or etc just use it to remove the action of your choice below. I wasn’t sure which emails you wanted stopped so i included all but obviously just choose what you need.
If you are doing the import programmatically then you could just include the remove_action lines of your choosing while running the import as well.
add_action( 'woocommerce_email', 'unhook_those_pesky_emails' );
function unhook_those_pesky_emails( $email_class ) {
/**
* Hooks for sending emails during store events
**/
remove_action( 'woocommerce_low_stock_notification', array( $email_class, 'low_stock' ) );
remove_action( 'woocommerce_no_stock_notification', array( $email_class, 'no_stock' ) );
remove_action( 'woocommerce_product_on_backorder_notification', array( $email_class, 'backorder' ) );
// New order emails
remove_action( 'woocommerce_order_status_pending_to_processing_notification', array( $email_class->emails['WC_Email_New_Order'], 'trigger' ) );
remove_action( 'woocommerce_order_status_pending_to_completed_notification', array( $email_class->emails['WC_Email_New_Order'], 'trigger' ) );
remove_action( 'woocommerce_order_status_pending_to_on-hold_notification', array( $email_class->emails['WC_Email_New_Order'], 'trigger' ) );
remove_action( 'woocommerce_order_status_failed_to_processing_notification', array( $email_class->emails['WC_Email_New_Order'], 'trigger' ) );
remove_action( 'woocommerce_order_status_failed_to_completed_notification', array( $email_class->emails['WC_Email_New_Order'], 'trigger' ) );
remove_action( 'woocommerce_order_status_failed_to_on-hold_notification', array( $email_class->emails['WC_Email_New_Order'], 'trigger' ) );
// Processing order emails
remove_action( 'woocommerce_order_status_pending_to_processing_notification', array( $email_class->emails['WC_Email_Customer_Processing_Order'], 'trigger' ) );
remove_action( 'woocommerce_order_status_pending_to_on-hold_notification', array( $email_class->emails['WC_Email_Customer_Processing_Order'], 'trigger' ) );
// Completed order emails
remove_action( 'woocommerce_order_status_completed_notification', array( $email_class->emails['WC_Email_Customer_Completed_Order'], 'trigger' ) );
// Note emails
remove_action( 'woocommerce_new_customer_note_notification', array( $email_class->emails['WC_Email_Customer_Note'], 'trigger' ) );
}