I finally got around to switching the DNS servers for hrtrust.org with my registrar last night. Hurrah!
This was a pain because I forgot that I needed the site to open up at the Liferay portal (D'oh!) and also didn't appreciate that the mail (MX) settings would switch too. Hence I surprised myself three times:
1. It all worked, almost instantly, as proved by www.pingability.com
2. ..but it directed www.hrtrust.org to the Apache standard pages
3. ..and all my email accounts stopped working
So, as is my usual practice now, I read as much as I could find in the "How-to s" on the Rimu site, tried a couple of things then logged a support ticket with them and waiting for them to fix it. As usual, I get a response very quickly, the work had been done (some minor config as described at http://rimuhosting.com/mod_jk2.jsp) and now hrturst.org resolves to the portal without the ports appearing in the URL.
With the emails, I managed to fix that myself by re-re-re-reading stuff about Postfix and Dovecot on the Rimu site. I had in fact set everything up correctly the first time but missed one essential re-start command and caused myself an hour or two's heartache. Anyway, the portal and the pop email works fine now although the mail client packages (Outlook/Express/Thunderbird) all needed some minor adjustments to cope with the new host.
I'm sure I will have missed something else but we'll see what happens over the next few days.