Hello, I would like to submit a patch to allow users to change the priority tag's form entirely. While it has been working for my use-case i.e basic operations inside org buffers and org-agenda, it is not perfect and there are some bugs that remain when using more advanced features with different tag forms (mine is `_p' where `p' is `[1-9]'), that I am not competent enough to solve. However I believe there are no breaking changes if the user does not modify said tag form. If there's any precision I can add, please let me know.