Pretty much,
The accessiblity block's repository is at https://github.com/marxjohnson/moodle-block_accessibility
If you sign up for an account, create a fork of my respository (with the "Fork" button at the top of the page), then apply your changes to that fork (clone the fork's repository locally, apply your changes, commit, push), it would create a nice link between the original and the modified version.