There is no evidence of any canon violations. period.
What we do know, that the Romulans travel back through time (decades prior to TOS) and cause significant damages.
Once they go back in time the slate is wiped clean. There is at that point forward no canon to violate, we are set up with a new timeline of events and possibilities (ie Yesterday's Enterprise, which the writers even have mention in some interviews).
That causes things to change both on personal levels, but on far larger levels.
Just like how not having 1701-C made the federation more militaristic, changed costumes, and set designs, ect.
This situation allows the same, but on of course a budget where they can truly change everything they wish.
The only things that can be a violation of canon would be events that occur prior to the Romulans going back in time. And so far, we have seen nothing in footage that predates when the Romulans travel through time (perhaps Spock has a child predates this). But nothing we have seen of that shows any errors.
So we can have the (as adults) know who Romulans are, we can have changes in design (on every level) we can have even changes in basic character (as character is formed by events, and on a personal level who knows how many events have changed, could be minor in some cases or could be huge). We could have the Federation a very military like organization. We can have characters who are of different ages (as parents might have conceived at a different time, with the changes in the time line).
Literally every single references point can be changed and not be a violation of any thing. As long as the material before the Romulans travel through time doesn't violate anything. And really we know almost nothing about that time period.