How best to stop Portugal's decline?

In the mid-16th century, Portugal was on top of the world. Its colony in Brazil (though brutal and plutocratic) was thriving, it had a near-monopoly on African portage, and it was the first European country to have a stable foothold in India. But throughout the 17th century it declined, and eventually was reduced to a second- or even third-rate colonial power. What would be the simplest and most effective PoD to stop this and keep Portugal on top of global trade?
 
Have Cardinal King Henry name an heir.

-avoids Spain taking over which prevents England and the Netherlands from powerslamming Portuguese ships and colonies to get back at the Spanish
 
The Portuguese actually win the War of the Castilian Succession and take all of Iberia. They then utilise a mode of commercial colonial expansion that is not based on quick conquest but only gradual colonisation. They also decide not to take possession of the Holy Roman Empire.
 
The Portuguese actually win the War of the Castilian Succession and take all of Iberia. They then utilise a mode of commercial colonial expansion that is not based on quick conquest but only gradual colonisation. They also decide not to take possession of the Holy Roman Empire.
The new country christened Spain moves on to be a dominating world power
 
The Portuguese actually win the War of the Castilian Succession and take all of Iberia. They then utilise a mode of commercial colonial expansion that is not based on quick conquest but only gradual colonisation. They also decide not to take possession of the Holy Roman Empire.

Aragon was the male line part of Spain and they still became Castille junior partner. If Portugal won here they would just be Aragon in the situation
 
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