It requires some tinkling because Samsung disabled this native Android functionality (wtf?!).
In any case, the method works and my phone can breathe again.
Instructions
Edit, 2018-03-19: Now the phone provides the option to add an SD card as an internal storage. However, be careful to perform the data migration after formatting the card. This will move the data and make pointers for the data folders. Otherwise, you may end up with the card formatted but not being used by the system as the data folders still point to the phone's memory card.
In any case, the method works and my phone can breathe again.
Instructions
Edit, 2018-03-19: Now the phone provides the option to add an SD card as an internal storage. However, be careful to perform the data migration after formatting the card. This will move the data and make pointers for the data folders. Otherwise, you may end up with the card formatted but not being used by the system as the data folders still point to the phone's memory card.
