Convert → Tag - File name append an E for explicit

For songs with the “Explicit” tag, a feature for automatic naming can be added.

This Image AI genereted.

You can add more or less any string to the format string so that it would not be necessary to implement a special treatment for particular fields.

You could append your format string with
['['$left(%rating%,1)']']

AFAIK there is no standard field called RATING. If you want to add the "excplicit" property to a file, then the field ITUNESADVISORY would be the correct place.
So I doubt even more that a special function would be added for a user-defined field.

Alternatively, you can Filter for tracks with an "Explicit" RATING and then add an [E] to the end of those filenames.

Format string:
$num(%track%,2)- %artist% - %title% '[E]'

this is what i do with explicit song titles

%artist% - (E) %title% %smyr%

or

$num(%track%,2)-%artist% - (E) %title% %smyr%

this way they are easy to spot and either use or forget during playback

note: smyr is a tab that i created using ($right(%year%,2))