you do not need to change anything in the BtS exe - it already recognizes large memory addresses - I do not know how large since this flag is designed for up to 3GB (from the standard 2GB) in 32bit operating systems. However I guess it will use as much as it needs to with your system
edit: note this means 3GB used by the game not overall...
edit2: oh I found it:
- A 32bit process compiled LARGEMEMORYAWARE running on a 64bit x64 Windows OS can address 4GB of Virtual Address Space.
So BtS will use up to 4GB of RAM - anything above that is for other programs