Unfortunately there is no such feature.
If you really wanted this, you could write a “converter” (with the yaml as input), or if the Thing is already loaded in the UI, simply tell it the thing uid and generate “.things” code for it.
Many people here prefer the UI way of creating everything (things, items, rules). However, I am a fan of textual config for all those. You’re right about being able to perform mass changes more easily, but I went one or two steps further. I programmatically create them!
This was my earlier attempt at dealing with this: Another Things and Items file Generator
Today, I still use a yaml file as the “list” of my “devices”, but instead of generating .things and .items files, I create the actual Things and Items at runtime.