This page describes how you can export a scene from Sequencer as an FBX file and make alterations to that file inside a third party application like 3dsMax or Maya.
Once satisfied with your changes, you can then import the FBX file back into your Sequencer scene in Unreal Engine 4 (UE4) along with your updated changes.
There are some caveats to this process to be aware of that you should keep in mind:
When exporting, you can export all the objects in your scene with animations to your FBX file.
Importing FBX files will only import animation. It will not create new objects.
Export/Import does not work with Master Sequences, Shots within a Master, or Subscenes.
Make sure that your time settings in your third party application matches the time frame used for your scene in Unreal Engine.
As long as you export from a source Level Sequence and not a shot that sits inside a Master, and are only altering the animation of existing assets, you will be able to import your changes directly back into your scene inside UE4.
Also, using the same time frames in both UE4 and your third party application will ensure that they line up and that the imported scene is not resampled at a different time rate.