Hey Twibbz, I set up a material the same way you did and set up my blueprints this way.
Create a new variable of the type “MaterialInstanceDynamic” and leave it’s default value empty, then use a “Create Dynamic MaterialInstance” to set your material to the newly created variable, that way your variable can then be used to set it’s scalar parameter.
Here you can see the emmisive multipler at 1
And here it is being set higher while being updated in the editor
