The way You presented here is not only tedious, it is also blocking any option of reimporting assets.
What You are looking for is post_import tool scripting. Create new script :
And than You can manipulate the root ( scene ) any way You want, but You have to return it. For example :
Or manually rechild mesh instances to new custom body and so on, You will figure it out :)
Now You just place this script in Import Settings in custom
script slot and press