Invasion cb shouldn't usurp titles from other cultures.

In the current version of the mod, when using the Invasion cb the invader has the ability to usurp the titles of all of the landed characters that aren't of his culture group. I think that the said feature is OP and not canon friendly, since we have an example of the ironborn conquering the riverlands during Harwyn Hoare's invasion. During which as we know most of the riverlords retained their titles in spite of obviously belonging to a different culture.

Suggestion: add a game sub rule to the invasion cb rule section that disallows lesser title usurpation from other culture characters.