There is a proven app available in Sales category of Apps Store to accept and manage pre-orders easily created by our team:
Pre-Order Manager. Shopify Preorder App! Manage Pre-Orders easily, customize the button, description, style for certain products/variants or the whole store.
And here is a list of its features:
✔️ Automatic change from “Add to cart” to “Pre-Order” button for out of stock products
✔️ Scheduling of pre-orders for products/variants
✔️ Limit manually the number of pre-orders
✔️ Geo-location settings
✔️ QuickView integration
✔️ Fully customizable button design and texts
✔️ Compatibility with ANY theme
✔️ 100% Mobile friendly app
✔️ Fast and Free support
I had a suggestion for you for adding 'Pre Order' labels to your product images. There are apps on the shopify app store that allow you to add product labels to your stores. You can pick the ones with pre-order tags. I am adding examples below that I thought would look good but there are other options - in terms of colours and text which you can always check here.
In these kind of labels you can easily edit the discount value without any development effort at all. It's a simple 3 step process where you select your image, select the label and then apply the changes.
I hope this is useful for you.
If you have questions about the app, feel free to reach out to me. :)