Can I set up a fixed value (fixed price) discount?
Yes, BYOB can support a fixed value or fixed price discount.
By default, Shopify only supports fixed-amount off, percentage or buy x get y for product discounts. There is no way to set up such a discount in Shopify.
BYOB uses variants to adjust to a flexible bundle price. As a result, you can set up discounts like any 3 for $X in a collection. You can select the discount type of Price in the app.
BYOB is one of the very few Shopify apps that can do so.