1. Install the licensed version of the game (temporarily). I recommend to make it on another device, just in case.
2. Link the game with FB. FIRST LINKING MUST BE ON LICENSED COPY TO AVOID BAN.
3. Uninstall the licensed app if you want - no need it anymore.
4. Go back to your main device with the Platinmods version of the game already installed (i.e. the <3.9.1 version).
5. Link the game from Step 4 with your account. Overwrite the linking if it prompts.
6. Install the 3.9.1 version over the existing one.
7. Launch the newly installed app and unlink from FB to avoid ban.
8. Play!
9. When the next updates will come, quickly repeat Step 4-7.