Our script is here: https://github.com/enovation/moodle-url_change . If you decide to do Moodle admin tool for 2.8 it may be worth moving some code into a shared library to share the code - as we will definitely want to use it across all Moodle versions.
cheers
How does your proposed tool differ from tool_replace in standard Moodle? Wouldn't it be better to improve that tool than to build a separate add-on?