First is my solution to your problem:
mark_new_chapters
Code:
## If true, when updating an epub that already has old chapters, new
## chapters will be marked in the TOC and chapter header by using
## chapter_title_new_pattern and chapter_title_addnew_pattern to set
## the chapter title.
## If set to latestonly, only new chapters downloaded this time will
## be marked (new) and existing chapters will have any (new) marks
## removed.
##
## mark_new_chapters can be true, false or latestonly
mark_new_chapters:false
This is exactly what I am looking for, thank you!