Hi - every time you press the compile button, Psychopy builder creates a .py file file with the same name as the .psyexp file. This will overwrite if there is a .py file with the same name in the same directory.
This is currently a one way street because the builder components are standardised in XML format and are formatted as python code on compilation - going backwards on this introduces too many variables to deal with at this point, so you will have to repeat the changes every time you make a change in builder and then return to coder.
So in short:
- If you are using builder, make sure you are really happy with your builder format before moving to coder
- Keep backups of your .py files whenever you make drastic changes in builder
- Become familiar with the coder view so you can rely less on builder