Can we update the order status in Miva after the order posts to NetSuite?
Yes, when an order is synced from Miva to NetSuite for the first time, the Order Status changes from "Pending" to "Processing". Miva uses status IDs but shows it to the user in the Miva admin site as words. Pending is 0, backordered is 201, shipped is 200, processed is 100 (see https://www.miva.com/forums/forum/online-merchants/miva-merchant-5-5/113237-order-status-types-and-numeric-values). Relevant settings: MivaStatus_Processing & MivaStatus_Shipped.