Microflow and Before Commit Event on an entity used to calculate data on commit

Let's get a very simple example. I use a Microflow to calculate and persist a simple calculation such as Attribute3 = Attribute1 + Attribute2 .  So, in the Microflow, I calculate the value and change the Object using a Change Object Activity. I believe this Microflow needs to be called as a Before Commit Event on the Entity and not a After Commit Event.  However, the Entity Event Handler needs to receive a boolean as answer.  My question is How can I return such a Boolean value from a Microflow .  
1 answers

If the goal is to make sure that Attribute 3 always contain the riight value of att1 + att2 it does not matter if you use a before or an after commit. You also could use a calculated attribute allthough that one depending on the situation could give you a performance hit. And you could just fill the endpoint with a true value as the return value (right click the endpoint and change the nothing to Boolean as the return value).