Hi, my dear Divi Manic,
As you I love to work with Divi, for many reasons.
For example in Divi is possible to have a fixed header that changes when you scroll down.
Another one is the new Divi Theme Builder, introduced with Divi 4.0.
Unfortunately, in this moment, if you want a custom header (built with the new Builder) that changes when you scroll down you need a trick!
And here it is!
To help you to implement in your layout this magic effect, instead of to explain how to do, I prefer to create a simple file you can download and install easily in your library.
Then you can customize it as you prefer.
To create my file I followed the instruction written by the great Ania Romańska (you can read her article here).