you could also accomplish this though thee use of a scalar parameter and a set scalar parameter node. basically in your material you would multiply you emissive color by the scalar parameter value, so if you multiply by zero then there would be no emissive but if you multiply by 100 then there will be. this also will allow you to control how intense the emission is. then in your actor blueprint you would just call the set scalar parameter value. you need to make sure the material is equipped and that the parameter name matches exactly. below is a picture showing the basic setup and the nodes. in my test setup i made the material then connected the set parameter to a timer and a flip flop to create a flashing light.
