If you've appointed an advocate via Vakilpatra, another lawyer from the same or High Court can indeed represent you. This can be done by terminating the current advocate's services and engaging a new one, or by appointing a joint advocate with a No Objection Certificate (NOC) from your current lawyer. If both advocates are from the same firm, formal additional paperwork might not be needed, but if they are individuals, an additional Vakalatnama is usually required.