Reusing adopted storage
It works as expected. After wiping data partition and rebooting to system I made encryption of data partition as I always do. Then again reboot to recovery. I copied encryption key for sdcard (with the same content, I didn't format sdcard) to /data/misc/vold and make sure that file belongs to root.

After rebooting to system again I didn't have any notification about formating sdcard. One thing I had to do: move data to sdcard. And after this step, I can see all my content on sdcard, which was mounted as adopted storage.