Is there a way to set up a discount password for my products? So I can give it out to certain people to use it when they buy my products?
I don't believe there is. However, you can set up a separate project, with a unique price, and give that link out only to those you wish to have the discount.
You need not add an ISBN to this project even if it is on the copyright of the interior. In other words, upload the exact same files as your public, matching project.
If you set the project to Direct Access, only people you send the link to will be able to see the discounted book. People searching for the book will not find it in the bookstore when they search for it.
While we don't have the ability to set up a discount like you're describing, there is a way to create a discounted purchasing option for specific readers.
What you'd do is create a new project, making it identical to the original. You won't want to add an ISBN, as this book will just be sold as the "Discounted" version on Lulu.
Set the price for the this book as you'd like it to be discounted.
Set the Access to Direct Access. A book in Direct Access can only be found through a URL (which you can copy from the product page in your account).
You can provide this URL to customers you'd like to provide the book to at a discounted price. You can always change to Private Access when you don't want the discounted book available, and the regular book will remain available without being impacted.