How to execute a script in mp3tag

Export scripts create external text files - so they do not change anything in the tags.

See the HowTo-FAQs on how to create a new action:

To assign a value to a field, use an action of the type "Format value", in this case for COMMENT:

Yet, I find it strange to write such a statement to a field - wouldn't it be a better step to filter for such files and then run an action or something to solve the problem? Because, I mean, what will you do with the information in the comment?

This filter would show you the files with longer titles:
"$ifgreater($len(%title%),30,yes,no)" IS yes