[JimmXinu]

The conditional part of a in/exclude_metadata_pre line (after &&) uses the same routines to get metadata values as everything else. Which means replace_metadata has already been applied to rating when the warnings _metadata_pre line is applied.

The wiki page mentions that for replace_metadata but not for in/exclude specifically:

NOTE: The way it works is that include/exclude_pre then replace_metadata then include/exclude_post are applied to each metadata entry as it's used, not all metadata as a whole. When using replace_metadata conditional clauses (see ReplaceMetadata), be aware that the include/exclude_metadata for both pre and post will already be applied to the metadata entries you are using in the conditional.

I will update that wording. Changing the behavior is a huge can of worms I'm not opening.

FYI, warnings is a standard metadata entry, you don't need to use add_to_extra_valid_entries:warnings. And be aware that extrawarnings is not universal, there are only a handful of standard metadata entries that have extraX settings.

Here's a solution that works for me:

add_to_extra_valid_entries:rating_raw
include_in_rating_raw:rating.NOREPL
include_in_warnings:warnings,"CAUTION"

exclude_metadata_pre:
 warnings==CAUTION&&rating_raw!=XXX-I

add_to_replace_metadata:
 rating=>^XXX-I$=>NC-17

I've created a raw copy of rating, replaced the extrawarnings line, and matched only "XXX-I" as an entire string. So if "XXX-II" shows up, it doesn't give you "NC-17I".