portupgrade MAKE_ARGS issue

[Kareem Dana]

I'm trying to become comfortable with portupgrade and I'm upgrading
p5-Mail-SpamAssassin as a test. It has several config options that can be
set with 'make config'. One of them is AS_ROOT, defined in the Makefile as
WITH_AS_ROOT. By default this option is enabled. I would like to use
portupgrade MAKE_ARGS to disable that option and I can't figure out how to
do that. I have tried

MAKE_ARGS = {
'mail/p5-Mail-SpamAssassin' => "WITHOUT_AS_ROOT=1',
}

and also WITH_AS_ROOT=false, WITH_AS_ROOT=

My initial thought is that SpamAssassin has WITH_AS_ROOT enabled by default
and it never checks WITHOUT_AS_ROOT, only whether WITH_AS_ROOT is defined or
undefined, so I would need portupgrade to undefine WITH_AS_ROOT which I
don't think is possible? Am I correct, and if so, that means the issue lies
with that specific port?

In general, if a config option is enabled by default, I should be able to
set WITHOUT_OPTION=1 in the MAKE_ARGS section and if a config option is
disabled by default WITH_OPTION=1, correct?

Thanks for helping me out,
Kareem Dana