Does this null XenForo or bypass the licence check?
No. It removes one line of output from one admin template. The licence check itself,
the branding check, and the invalid-licence errors are all untouched. It cannot
unlock updates or support because those come from XenForo's server, not from your board.
Will it hide a genuinely invalid licence or missing branding?
No. Those go through hasLicenseErrors(), which this add-on doesn't touch at all.
They will still be reported.
Does installing or uninstalling affect my data?
No. There is no Setup.php and no PHP in the add-on, so nothing runs against your
database beyond XenForo's own standard add-on bookkeeping — one xf_addon row, two
xf_template_modification rows, and a template recompile. Uninstalling removes those
and restores the original output.
Will it survive a XenForo upgrade?
If a future release rewrites the warnings or full_status macros, the modifications
will report as no longer applying under Appearance → Template modifications. They
fail visibly rather than silently, so you'll know.
Why not just renew?
You should. This changes nothing about your licence status and doesn't pretend to.