When there you may edit to your heart's desire, although I recommend copying and pasting between a proper text editor of your choice (I like Notepad++). Also, there's an "Advanced" button in the Text Edit window, all this does is change what the helper text shows (that is, the text that appears when your mouse hovers over a button or part) to text that will be of use if you want to text edit. Namely, it says the actual name of parts, which you'll need in the text editor, and it shows the parent of a piece which is just to show you how it works.
Have fun! and be careful, one wrong letter and the level won't load properly

I made a few bug fixes as well.
~MD