Ok. I dont know bleep about G Codes but if your interface is anything like mine, this might help you..
In my interface program.. I can use a GOTO command to jump anywhere..
But, when I write a program into a text file, I must use the JUMP command inplace of the GOTO command..
IF THEN still works fine..
Did this help you? I dont have the pro version.. Mine is just Graphical OI.