The main differences between Pro and the BS2, other than Pro programs are faster and can be longer, are some additional instructions and some changes in the way some of the instructions work. There is no nibble data type in Pro. Since Pro can access more RAM, it is usually not a problem to make these byte type variables. The MAX and MIN operators have been altered to work in a more standard manner. Also, since expression operators have precedence, the ordering of math instructions or the addition of parenthesis to specify the order of execution should be examined.
Any program code can occur within the structure.
There is also a way to tell Pro what clock oscillator you want to operate at instead of the 4Mhz PBC expects. The standard PicBasic Compiler is still quite capable. If you need maximum BS1 compatibility, or you are using only the smaller PICmicros, the PicBasic Compiler could make alot of sense.