exim PORT -- when to use? when to 'go manual'?

[snowcrash+freebsd]

hi,

i've built-from-src and used-as-standalone exim on many boxes.  no problems.

i've just installed exim on a "small" freebsd-based router -- via
PORTS install -- as a sendmail replacement. no probs, either.

now, I want to "upgrade" exim on that router to add 'just'
DNSBL-filtering on the router, and have it function as a transparent
gateway to another lan-based, exim router.

do folks recommend still using the PORT install?

iiuc, general advice for PORTS is "use the port, don't touch the port" ... true?

if so, how/where do I configure exim if not mod'ing the port's MAKEFILE?

if not, is the advice, then, to build/install exim from source "by hand"?

thanks!