Hello Kiran,
Please refer OSS note 1694267 - BAPI_ALM_ORDER_MAINTAIN not for work orders
You can use BAPI BAPI_PROCORD_CHANGE (for process orders)
BAPIs can change the order header. Use the remote-enabled function module CO_SE_PRODORD_CHANGE to change the order header, sequences operation etc.
Best Regards,
R.Brahmankar