Normalizing content ratings for US region Not Rated when other regions do have PG ratings

I have separate Plex local accounts for my kids, and I set content rating filters.

Some movies show up as no rating, and I have to manually set a rating so the kids can watch it, if age appropriate.
Some movies show up as no rating, and the content is clearly mature, and when I look on IMDB, the US rating is not rated, but many other regions have some form of usable rating.

I considered using unrated as a category, but the usage of unrated is inconsistent.
I used ExportTools to export the movie list to excel, the rating filter shows a mixture of no value, “unrated”, “nr”, and “not rated”.

Is there an easy way to batch modify the ratings to a consistent value that I can use for filters?
Is there a way to configure the Plex movie scraper to properly set the field, by e.g. looking at TMDB and IMDB, and by normalizing the not rated value?

As an enhancement, for any unrated content, look in the parentalguide section on IMDB, and pick an appropriate mapping.

E.g. not rated in US but mature in other regions


E.g. rated PG by IMDB but no rating in TMDB


E.g. rated R by IMDB and no rating in TMDB