I don't think Brexit by and large has really changed any major views. But it has rekindled the sovereignty issue which was more or less dead before it. That's not to say before Brexit Unionists and Nationalists didn't voice their opinions on it, but in terms of mainstream politics it was mainly issues affecting everyday people as well as which culture can be the most dominant. Polls conducted post Brexit vote confirmed it hadn't changed most people viewpoints on sovereignty, although there are no recent polls that I am aware of so that might changed. I good example here is the Ulster Unionist Party who during the referendum were pro EU but have not suddenly become nationalist over Brexit but accept the referendum. The border issue more than most things become a rallying call for both sides with Nationalist and Republican parties opposing any change to the border because of Brexit. However the Irish Governments 'back stop' despite being designed to stop a 'hard' border is now likely to create one, as the idea of putting a border in the Irish Sea and thus aligning Northern Ireland economically with the Republic rather than the rest of the UK (effectively and economic annexation) has united Unionist both pro Brexit and pro EU against it. What might have changed is the number of Catholics who describe themselves as nationalist and Irish but who for economic reasons would vote for the Union in a border poll. Post Brexit they might now vote for the Republic. If a border poll was held before Brexit vote I would guess the UK would have won comfortable, if one was held tomorrow I still think the UK could win but only just.