It is sometimes necessary to modify the contents of an installed package. If you find that you have to do this, you should always install the package with configure rather than package. In the unlikely event that you are configuring Python, for instance, you should install it with, for example,
configure('BU:Python | version("2.3.3")')
rather than with
package('BU:Python | version("2.3.3")')
Pacman installs the package the same way in both cases, but the configure syntax let's Pacman know that
if Python is updated, for example, your package must also be re-installed.