Unfortunately, there’s not a way to override events bound to components in child blueprints. However, if it’s a normal event not associated with a component (events without a component in parenthesis after the title), you can call directly to the parent by right clicking on the event in the child, and selecting “Add call to parent”. When you copy/pasted the event from the parent to the child, what it did was actually make a new custom event (you can tell by the yellow “Custom Event” text under the title). That means you could call that event, but it’s not automatically hooked up for you. We do this so that if you’re moving lots of code between blueprints, you can see how things were hooked up previously, and it makes refactoring a bit easier.
In the future, there are some changes happening that will allow you to do this more directly. However, for the moment, it’s best to add a new function or custom event that you call directly from the event. So, in your case, you’d have your OnComponentBeginOverlap call directly to a new function you create (e.g. “DoStuff”), and then override DoStuff in your child blueprint. That will give you the flexibility you want, but working within the current system.
Hope that clarifies things a bit!