The web UI is very convenient for somebody learning to write pistons, however as a software developer it would be really nice to be able to open up the code in my favorite text editor and make modifications. Is anything like that possible?
There’s no manual piston editing available at this time. The web gui is all we have.
To expand a bit since this is a common question, the source code view is just a display layer; it is built from a compacted data model which encoded as JSON is not impossible for a human to read but very close. The smart apps and the web UI both understand this data structure but most of the properties are named with a single letter and intermingled with data specific to your install, like device and contact IDs.
Hopefully this helps to understand why this is not as simple as making the code view text-editable. Without the limitations of ST groovy any future rewrite would be able to use a more reasonable data structure that would make it easier to support alternative editors or translation from source code.
Edit piston manually and also location mode