It could be updated by AppsAudit or tce-update if it is a tcz extension.
When loaded it could overwrite /opt/tcemirrorlist
This way no special button is needed, and it gets updated with new mirrors any time you update extensions.
If you accidently trash the file or forget to add it to .filetool.lst, you can just reload the extension.
One could add it to onboot, or ondemand if one wished.