Hi lad! I had the same problem and couldn’t find any examples or complete information, only a small entry in 4.25 Release Notes:
New: Material Layer Improvements (Beta)
Material Layers have been updated with the ability for Blueprint functions to modify Material Layer parameters at runtime and improved behavior when propagating layer changes from a base material to derived ones.
I’m still pretty new to this engine, so i just start to messing things until i get it work like this:
As you can see, i use Dynamic Material Instance to change parameters values by setting them by Info. I did it not only in Event Graph, but in Сonstruction Script and it work just fine!
I hope I am not too late and you will succeed!