I need to remove a master file from an esp - can this be done at all? For example: I have a cleanup file which removes certain objects from the game, like litter and papers - when I originally created the esp I used all 5 DLC's, now I want to remove The Pitt from the esp - as long as it remains the game won't load, since I have removed The Pitt.esm etc from the game folder.

Use FO3Edit 'Clean Masters'. Also make sure you remove all the references to it.

Thank you. I'm also just working through the PDF manual of the FO3Edit - it's a monster alright!