Modding, copyright, and related issues.

1. In the psatkha scenario, when some PR person or just support answers and expresses their opinion that basically, you can use the resources, yes. But no one will give official permission.

In principle, this is already something, at least. I mean, given the impossibility of getting something better. That is, it is not a fact that they even have a person authorized to give such permissions. Who is in charge of the copyrights for the resources? Perhaps there is a mess there, and no one is really in charge, and the resources simply circulate between development teams within the series.

Added 2 minutes ago

They replied that it is possible to use content in non-commercial MODs within the Universe created by Ubi! That is, from 6 and 7 to 5, or from 5 and 6 to 7, or from 5 and 7 to 6... I didn't ask about Dark Messiah, but it is clearly the same here!

This is good, of course. But it would be nice to confirm such things with screenshots of the correspondence (specifically screenshots, not text quotes) and it would be nice to put these screenshots somewhere in a prominent place on the forum.
And the more English the dialogue is, the better.

In general, it is better to contact the English-speaking support again and ask about all three games, and then attach screenshots of the correspondence in a prominent place.
Ideally, also ask him if he is sure that he can give such permissions, and if not, who to contact.

Added 7 minutes ago
Honestly, after googling all this, I only found an article from Ubisoft for YouTubers. It was something like this: use it as you like, but without racism, sexism, and homophobia, and it was also written that Ubisoft still reserves the right to ban a person without explaining the reasons.
Unfortunately, I didn't find anything more useful.