I've set priority years ago, via package customiser rules and it used to work aok, but I haven't been using JD at all in the last year or two so not sure what your doing wrong or if a bug exists.
For memory all links get renamed to uploaded.net
Code:
link.setUrlDownload(protocol + "://uploaded.net/file/" + id);
yep
you could email your package customiser rule to
support@jdownloader.org and we could test them with some provided test links.
raztoki