I have an solution, even tho it will not work somewhere else
I think that the Brazilian imperial family needs some advertising to broadly promote the fact that some slave owners, who were pro-republican, were angry when the monarchy sided with anti-slavery; however, I think the advertising needs not just to focus on the main topic, but also on global anti-slavery movements. Maybe this advertisement will still convince a small number of people, but who knows then? Because in my opinion, Brazil has suffered many corrupt heads of state, the previous one was also far-right, so it is probably viable that the monarchy will gain more support; however, right now, the movement is small, but who knows then?