Alternate checks for reinjected mail

I am running SpamAssassin via an after-queue content filter. After
processing, the filter reinjects the message using the sendmail command,
thus subjecting it to redundant header/body checks. The first line in my
header_checks is:

/^X-Spam-Flag: YES/ HOLD

This allows me to review messages marked as spam, so the redundant
header check does serve a purpose. Is there a way to bypass all checks
after reinjection, but specify an alternate header_checks file that
would continue to perform this role?

My master.cf content filter:

spamfilter unix - n n - - pipe
flags=Rq user=spamfilter argv=/usr/local/bin/spamfilter.sh -f
${sender} -- ${recipient}

My content filter, spamfilter.sh:

#!/usr/bin/bash
/usr/bin/spamc | /usr/sbin/sendmail -i "$@"
exit $?