Locally modifying ports

[Chris Ross]

  So, I've been a NetBSD user for many years, and am looking more
at FreeBSD now.  Trying to build myself a system, I find that I have a
long-held delta to a package on my NetBSD system, and I keep it
in a patch-local-* file in NetBSD pkgsrc.

  I can't figure out if FreeBSD ports has a way to keep and automatically
apply "local" patches to ports.  I want to modify the way the internals of
a package/port operate, and not in a way that makes sense to move up-
stream.  It's just my preference.

  Is there a way in FreeBSD ports to keep a "make this change to the
source code after extracting and before compiling" type of thing in the
tree?

  Thanks....

              - Chris