What if you serve GoogleBot one title tag and GoogleBot Mobile a different title tags/attributes? Google’s John Mueller said that Google would likely just ignore it, or maybe just pick one? Here are the tweets:

We’d probably just ignore it.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) September 28, 2017
GoogleBot for mobile and desktop are very similar these days and when Google goes full-on with the mobile first index then things will flip. So make sure not to try to play games with Google here, especially now.
Forum discussion at Twitter.