The comparison with Ireland is much different as the Portuguese from Metropolitan Portugal would not be a marginalised and disenfranchised people with a different religion and language and customs. That is not to say that revolts are not possible, particularly early on as the elite want Brazil to return to its pre-1808 mercantilism system. Early on in the 1820s you have two factions in Portugal, or rather in Lisbon and Porto. The liberal bourgeois whom would look to England for assistance and the conservatives backed by the powerful church and old nobility looking to absolutist France and Spain. The liberals are going to probably win out, but in return will have to give up an pretense of having he old order restored. A compromise might be a personal union, with joint navy, foreign ministry and common currency.
Revolts were not unknown throughout XIX century Europe, but usually they were relegated to Lisbon or Porto, as the rest of the country stagnated and the literacy rate was probably less than 10% outside of the cities. North of the Tagus River, the Portuguese economy particularly in the small towns and cities was economically dependent on the emigration to Brazil. The remittances sent from Brazil were so significant that as early as March 1875 Joaquim Pedro de Oliveira Martins, a deputy in the Cortes stated that Portugal was completely financially and economically dependent on Brazil. This only increased as Portuguese emigration there increased progressively, so much so that in 1890 when remittances were disrupted due to the revolution in Brazil, the lack of foreign exchange caused a financial crisis in Portugal. By 1910 in districts like Bragança one in six young men emigrated to Brazil with around one-third returning, many with small fortunes, building hospitals, schools and providing much needed capital to areas with a mediaeval economy. Between 1890 and 1930 alone over 1 million Portuguese left for Brazil. Any revolt might would seriously hamper one of the economic backbones of an already fragile economy.
My take is the Portuguese character would be even more fatalistic and resigned to their fate, not dissimilar to how many perceive of themselves as a tiny powerless nation within the European Union. Throughout much of the XIX and XX centuries it was said that Portugal needed the empire in Africa or else it would be reduced to a Spanish province, if they revolt they're left without that. The country produced little of value, and without coal, iron ore missed industrialization. The poverty can be reflected whereby 1930 its literacy rate the lowest in Europe than one-third of its people able to read or write. By comparison, Spain, Greece, Romania, Bulgaria, Poland and the USSR were all above 50% by that year, the only country in Europe with a less educated population was Albania. Lisbon and to a lesser extent Porto were able to modernize, but in the case of Lisbon much of this wealth came from the imperial economy and the civil service, banking and shipping linked to the colonial empire. By the 1920s, the diamond monopoly in Angola and the labour agreement between Mozambique and South Africa provided income directly to Lisbon. With the navy on the royal family's side Portugal would probably even lose the Atlantic Islands as these archipelagos would be even more dependent on emigration to Brazil than the mainland.
With enough autonomy and a greater reliance on settling much larger numbers Portuguese peasant families, particularly those from the islands in southern Brazil, I imagine this can function as a large safety valve for any revolutionary activity. One has to remember that between 1870 and 1930 the economically active population in Portugal continued to decrease to just over 50%, meaning there were not enough jobs to support the population growth. The government would probably set a larger budget to financially assist immigration to Brazil from Portugal, something that did not occur after 1822.
