I am attempting to read a RS232/USB input from a Gcode script. Is it possible to perform this from GCode or am I going to have to wrap it in python or something?
For reference, my algorithm is essentially:
-Perform some CNC movements
-Read/store/record variable from RS232 peripheral
-Repeat a bunch of times in marginally different ways
Gcode per se doesn't support reading anything from any peripheral.  Gcode is nothing more than a line-oriented textual machine command format, and is typically fed from a storage medium or file into an interpreter.  This interpreter determines the axes movements, usually incorporating some trajectory planner.  Then the interpreter emits signals to a peripheral device (LPT port, special card, etc.) that are fed to motor controllers.  So without more details, based on your question, I think you're going to need something else to handle any serial connection.  If you could clarify or add more details a solution may become apparent.
GCode and RS232