Appending to a parameter using postconf

[Robert Moskowitz]

Is there a way to append to a parameter using postconf.  If it is only 
in a version later than 2.6.6, oh well.  But the example is 
smtpd_recipient_restrictions which can have a long list and then you 
want to add a realtime black list check fqdn.

Also in this vein, can postconf -e 'parameter= ...' be submitted on more 
than one line, or with a long entry as above, does it have to be just 
one entry line.