I have gone through your query and you can try the Discount Depot App, it will be helpful to resolve both your mentioned queries. You can use it for displaying different prices to different customers based on the tags and while submitting the sales to POS you can use the same credentials which will auto apply the discounted price for the customer.
You can give it a try and let me know if you need any other assistance from my side.
Shopify Developer/Consultant If my suggestions are useful, please let me know by giving it a like or marking it as a solution. And if you want to customize or develop new feature on Theme or App. Skype:-ankit.thakur_5