Add to read-only fbx animation clips

I've been using 2d animation clips so far but now that I'm in 3d I can't animate additional objects other than the bones in the animation clips from the fbx format. How could I sync up a hitbox activating with my 3d animations or how can I send events in the same animation clip?
It would be too weird to make another animation clip or to activate those by scripts at the right time.

 

Ok I found that under the Animation tab there's a possibilty to add events and curves.

 

Why are the animation files read as fbx are read-only? Is there a particular reason?

 

see the answer in this thread
https://forum.unity.com/threads/extending-statemachinebehaviours.488314/#post-3596674