This is something that has bothered me every time I tried some Python scripting in Blender: if you use an external editor, your changes won't be automatically loaded. Script Watcher fixes that.
Isaac Weaver writes:
Hi, I just posted this on blender artists but thought I'd tell you about it too. It's an addon I developed to assists in the development of other script, specifically if you're using an external editor.
Basically, it watches the script you're developing for changes, whenever a change occurs it re-runs the script in blender. This allows you to save your file and instantly see blender update with the new version of the script.