No window dressing + South Africa propping up the colonial regime = when Apartheid falls, the colonies become independent and no you don't even get to fight their rebellion tyvm or the United Nations brings out the sanctionhammer. Especially as one million immigrants, assuming all the portuguese emigration of the decade moves there, just means 10% of the colonies are white.
Without Angola and Mozambique falling, Rhodesia will not fall as easily. Rhodesia really only began to suffer after Portugal pulled out of Mozambique in 1975 and they lost their main outlets for trade. Despite sanctions, Rhodesia's economy grew from 1966-1974 and the country managed to attract a net gain of white immigrants until 1975. Also, with Mozambique still under Portuguese rule, ZANU and ZAPU cannot use Mozambique as a base to launch raids into the country. This gives Rhodesia a much longer lifespan.
South Africa too will not have to suffer a border war in Southwest Africa, so they are much better off by being able to avoid conscription and a costly border war in Angola. Also, they could avoid many of the initial military sanctions by not invading Angola. On the other hand they may not be as self sufficient in the production of military hardware as they were by the 1980s.
Under what pretense would sanctions be launched against Portugal? Unlike South Africa and Rhodesia the country did not practice racial discrimination. Even Kenya's foreign minister criticised Portugal for being a colonial power in 1973 its government was not racist and Portuguese Africa was probably the most racially harmonious part of the continent.
Also, one has to remember that even the sanctions against South Africa were launched mainly because of its aggressiveness towards neighbouring countries. I cannot see Portugal launching attacks on any other country. Finally, sanctions would have to pass the security council.
Portugal, unlike South Africa was a NATO ally. The UK, US and France consistently voted against resolutions condemning Portugal in the security council. Other countries that were non-permanent members that generally voted in favour of Portugal were Latin American countries and Pakistan. Unlike South Africa, Portugal did enjoy cordial relations with much of the world including many non-European nations.
Finally, I believe you may need a math lesson. By 1974 Angola and Mozambique had around 800,000 European settlers combined out of a total of 15 million people. In addition there were another quarter of a million mixed race individuals and perhaps 35,000 Asians. If you added another million individuals you'd have 1.8 million Europeans not 1 million. This also assumes that these people would have no children, considering the rate of natural growth of the European population was around 1% per annum, its rather implausible. Below is a chart showing Portuguese emigration between 1900 and 1996. Please note that the figures are only for emigration abroad, since Angola and Mozambique were integral parts of Portugal they are not counted in the totals prior to 1975.
http://imigrantes.no.sapo.pt/page6Estatist.html
In fact, it is plausible that the European population could have grown something like this had the government been more open to it early on. Although Mozambique's European population would still only be 7% of the total, Angola's would have been 17% by 1970, the same as South Africa's.
ANG MOZ (figures in thousands)
1940 80 50
1950 175 100
1960 550 330
1970 1085 680
1980 1400 835