Part 1:
From the Python Docs:
Upon startup with the -s option, IDLE will execute the file referenced by the environment variables IDLESTARTUP or PYTHONSTARTUP. IDLE first checks for IDLESTARTUP; if IDLESTARTUP is present the file referenced is run.
IDLESTARTUP is an environment variable that tells the IDLE the location of a python script to execute on startup, as long as the -s option is given when you start the IDLE. Thus you need to edit the script pointed to by IDLESTARTUP or PYTHONSTARTUP, add the import ... statement, and use the -s flag to start the IDLE.
Part 2:
To add to the sys.path permanently, you can edit the same file we edited above (the file referred to by IDLESTARTUP or PYTHONSTARTUP, and do a
import sys
sys.path.append("...")
Note on Environment Variables:
To figure out if you have a IDLESTARTUP variable or PYTHONSTARTUP variable defined in Windows, you should be able to go to Control Panel > System and Security > System > advanced > Environment Variables.*
*(I'm not much of a Windows user, so you might need to seek out how to change environment variables in Windows on other questions or Google).
PythonGUI, are you talking about thePython IDLE? Or some other GUI?