This is the standard.
And this is the premium
The Premium substitutes a button from the Standard for the SD Card Slot. The buttons on the left also perform different functions. I imagine it is possible to modify both systems (chances are they are programmed with Java), but you will be limited to the capability of the hardware. The problem is, there is no way to access the APPS in the Entune Premium without that button. Unless the hardware allows you to customize what the buttons do by editing the software, you won't be able to get a standard to function like a Premium, and again, you have the memory issue. Chances are the Premium has more on-board memory to support the apps than the base stereo.
The Premium also talks to the Multi-Information Display. If you have the base gauge cluster, some functions and apps won't work properly (the Eco app pulls data from the Multi-Information Display as well as the PCM).
I will say this, if you pull it off, you should work for NASA.
I'm still waiting until a junkyard gets a totaled Corolla S so I can mod the flasher circuit to eliminate hyperflash with LED turn signals.