Hi,
I'm pretty new to gree so I'm not 100% on this but I *think* you can transfer the data as long as you have a passworded account. To upgrade your account to one that needs an email and password (these steps are for be my princess but it should be similar in another app if that's not one you play):-
1. Launch game app (Be my princess)
2. Tap home icon on the top right portion of the app screen (you will be directed to the Gree SNS app or Gree Platform)
3. Scroll down - see official user,click 's icon/avatar itself
4. Pop-up page will tell you to "COMPLETE PROFILE TO SEND FRIEND REQUEST" - a way of upgrading guest account
5. Another Gree screen would pop-up and will tell you to "UPGRADE" hit upgrade
6. Pop-up screen will provide a login screen with "guest player no. or the "nickname"
7. Enter email, password, and birthday then click "NEXT"
8. Check your email and enter the 4-digit PIN code sent to your email
9. A PIN code will be asked for you to "VALIDATE" account "email is now verified"
10. Account is now "REGISTERED", old guest data is in progress…
One warning though: If you have a different guest account for different games you will have to restart the others (This is unlikely though. If all your apps show up in the guest account apps section then you are using the same one for all of them and will be able to keep your progress)
Hope this helps :)