Robsato has enabled the upload of optional files and patches to his addon, so that would be the best way to go. I would still label it as a "Fan Update", but you can still have your own page for it, tag it as compatible with 4.1, have it show up in the updated list, etc., etc. Plus it will be linked with the original.
In order to do so, go to the
Optional Files tab of the download page and click on either "Upload Optional Patch" or "Upload Optional AddOn". They both do the same thing, it's just an internal flag for either link.
/edit: but first talk to Robsato about your changes. He was just active on the site today! Maybe he'll roll your changes into the main download or add you as a contributing author to the project.