can i rebuy the ps3 game to get access after transferring my current ps3 acc to ps4?

[Zumi]

Therefore, vice-versa if you transfer you can purchase a Playstation 3 version, so yes it does.

You can't assume the opposite is true though especially after you already entered a PS3 code and upgraded it to PS4. If you remember back when ARR came out people had to buy the PS3 version of the game to get collectors edition bonuses if they didn't want to do the digital upgrade because they couldn't buy the PC version CE and enter the code because SE system wouldn't allow them to enter another PC code.

The same thing could apply here, the mogstation site could see well you already entered a PS3 code before you aren't allowed to registered another one. This is probably due to the fact that if someone found a bunch of PS3 copies really cheap they could keep stacking the free 30 days on the account.

Due to the fact is says to play on both systems you must buy the PS4 version. Not you can upgrade to PS4 then buy another PS3 version to play on PS3 again.