DrByte, I just want to clarify to make sure I understand correctly.

I should take a copy of the define-pages-editor page and alter this as a starting point and
Then ammend it so that when it reads through the files it parses any instances of the define calls using parse function.
For each instance of define() I should create an input field (to allow the editing)

When submit, collect any changes and validate them (ie so no php errors etc caused) and then re-write the file the define statement came from?

Is this what you are saying or have I missed the point somewhere?

Thanks for you responses and help!