I don't really understand what you want, but I see two possible things you might want to check out. If you want to ...
1) ... set the compilation flags: use
# make config-recursive && friends,
2) ... change the internals of the port itself: write a custom patch.
1) setting the compile time options:
Usually, you set those things (compile time flags) when you run
# make config, (or
# make config-recursive, if you want to resolve for dependencies in one go as well) or a similar utility (e.g.
ports-mgmt/portupgrade,
ports-mgmt/portmaster), however, if that is insufficient for your needs, you might want to write your own custom patches.
2) writing a custom patch:
First, I'd check this out:
http://www.freebsd.org/doc/en/books/porters-handbook/slow.html and read as much as I needed, to know and understand what I'm doing.
I dunno where I read that, maybe in this very handbook (although I think it was the general FreeBSD handbook), after your patch is ready, just put it into
/usr/ports/<path_the_port_I_want>/files/, and the patch has to have a name of the form
patch*. When you run
# make, those patches will be executed in an alphabetical order.
So maybe name them like
patch-z-<my name>, so they won't interrupt any existing patches. So you can write a patch for the
Makefile, ordering it to remove any generated documentation. However, I would discourage you from doing that, unless you know what you're doing, because it's fairly easy to break your ports.
