I have found a way to re-import animation from Blender without lose anything.
The only way I found it: the first time that you import your model, remember to add it various animations, empty too(just create the animation name in blender ), then u can use “reimport with new source” option to each animation you have created.
Go Blender, doing new animation WITHOUT CHANGE THE NAME export, then reimport on specified animation in Unreal.
done.