I do a find (which I would also like to automate)
For examples of scripted finds: Scripted Find Examples
I would need to create a new related record in Mailer Action with the current date, media type sent (value list) and campaign it is part of.
If this data is all in the records of your found set, you might use Import records to generate the set of related records, mapping the primary key of your parent records to the foreign key of your child records. (Yes, you can use import records to copy records from one table to another i the same file just like you would for different files.)
You also have the replace field contents tool as an option for updating every record in a found set--either in the parent table or the child (import records produces a found set of the newly imported records).