After yet replacing a model just to add a few more forgotten or need morphs it would be nice if UE4 had a morph loader that can add a morph target after the fact. 
Can’t you just reimport your model? I believe if you had morph targets checked then it will update them.
That would be one way of doing it but 3ds Max only supports up to 100 targets and 3ds Max is not the only app that make them.