How to override method in frappe?

@rmehta The complete feature will be enable bold fields in pos.
or
For this current fix, we just need to update below code. and loop data (data is local storage customer list here)
Please advise on it.

def add_customer(data):
	customer_doc = frappe.new_doc('Customer')
	customer_doc.customer_name = data.get('full_name') or data.get('customer')
	customer_doc.customer_pos_id = data.get('customer_pos_id')
	customer_doc.customer_type = 'Company'
	customer_doc.vehicle_no = data.get('vehicle_no')
	customer_doc.customer_group = get_customer_group(data)
	customer_doc.territory = get_territory(data)
	customer_doc.flags.ignore_mandatory = True
	customer_doc.save(ignore_permissions = True)
	frappe.db.commit()
return customer_doc.name