It won't be "automatic", and it depends on what you have changed in SolidWorks.
It's easy to replace a solid part in Multibody: you just export a new STEP file and put the name in the right file solid block. So if you change the geometry of a part, you can try this.
If you change the material of a part, you can also manually change the density value in the file solid block.
It's much more difficult if you have changed the location, orientation, or types of the joints/mates. You can still manually change the tranform blocks and joints, but I'd guess it's not as easy.