Disclaimer: I did this 30 seconds ago, and had to share it and I'm not yet aware of the drawbacks. But as it only use legal dev interfaces, loss of data is the worst that can happen.
Prerequisites:
Phone using Android 6.0
SD Card that will get erased
ADB access (developper menu + usb adb enabled + adb authorized)
Commands:
macbook:~ jean$ adb shell
shell@p1
$ sm list-disks
disk:179,64
shell@p1
$ sm list-volumes all
private mounted null
public:179,65 mounted 9F29-15FD
emulated mounted null
At this point I have a SD formated from the phone. Old cards are public and SD card device id is disk:179,64.
shell@p1
$ sm set-force-adoptable true
set-force-adoptable should not be needed. But I'm lazy and I won't do it again to confirm, so there it is.
shell@p1
$ sm partition disk:179,64 private
That line repartition and format, it takes time.
shell@p1
$ sm set-force-adoptable false
shell@p1
$ sm list-volumes all
private:179,66 mounted 0ef3b40b-103f-4331-b0ce-92f105f8xxxx
private mounted null
emulated mounted null
emulated:179,66 unmounted null
https
/www.reddit.com/r/lgg4/comments/3z1bfi/enable_adoptable_storage_on_your_lg_g4_stock_no/
This is a win, the card is now mounted as private (internal).
Now, in Settings->Applications, you will be able to move even those apps that didn't want to go to external storage.