Hello Cheyennemtnman,
Thank you for interesting in our EShop Shopping Cart extension and submitting the questions here. Regarding your questions:
1. I am sorry but we don't have any hooks or the plugin that could be used to offer POS capabilites now.
2. For updating inventory, you can use our EShop Import Pro tool to update the data. So you just need to prepare the data from Excel / CSV file to update. You can read more about how to use EShop Import Pro here:
eshopdocs.joomservices.com/eshop-import-pro/how-to-import
Hope to hear back from you soon.
Sincerely, Giang