So I just edited the web form at gandi for the DNS of the .com address, sent a signed email to the 'change' bot at db.debian.org for the .net address, edited the configuration for bind, edited /etc/hosts, edited apache's httpd.config, and updated the IP address itself for the mail forwarder. Now all I need to do is wait for DNS to catch up :-/
Somewhat of a silly game, really. Maybe I should splurge for a real provider like Speakeasy?