The problem in your case is, that the syntax highlighting script for package uses a keyword (:h syn-keyword) and that always has priority before any of the syn-match or syn-region rules.

In your case, I would therefore simply use a matchadd() call like this:

 :call matchadd('Conceal', 'package', 10, 99, {'conceal': 'p'})
 :set conceallevel=2 concealcursor=nv

this needs a relatively new Vim version (I don't remember the exact patch level, but a 7.4.700 should work)

The problem in your case is that the syntax highlighting script for your package defines a keyword (enter :h syn-keyword for more details) and that always has priority before any of the syn-match or syn-region rules.

In your case, I would therefore simply use a matchadd() call like this:

 :call matchadd('Conceal', 'package', 10, 99, {'conceal': 'p'})
 :set conceallevel=2 concealcursor=nv

This requires a relatively new Vim version (I don't remember the exact patch level, but a 7.4.700 should work)