Ukrainians can hack American missiles and use custom firmware 😄 So the West can always say that Ukraine acted independently.
Of course, speaking seriously, the response to such actions might be the appearance of ballistic and other weapons, suspiciously similar to Russian ones, but not Russian, in places around the world and with parties where the West doesn't want them to appear. It won't happen immediately, it will happen gradually, but the result will be that no one will be safe.
The world your children will live in will be a very hot and 'fun' place.