Reinstall orphaned packages

Once a package is "orphaned", is there any way to reinstall that same version?

I have PHP 5.4.45 installed and my hands are tied ... I just can't upgrade to a later version until all the forum / CMS software I have installed fully supports it.
Other than to use SVN to roll the whole tree back a few months (and freeze it there), there's no way.*
PHP 5.4 End-of-Life was 3 September 2015 and well publicized.
If you are using software that can't run on PHP 5.5, 5.6, or 7.0, I'd say your software isn't being maintained.
I don't see how a vital forum/cms project would be in a PHP-5.4 only situation.

* and then you cannot use binary binaries; you'd have to build from source and I don't know how pkg would view the "future" versions of everything you didn't rebuild and reinstall.
Our ports tree works on the assumption that everything you have installed comes from the same "state" of the tree (from the same time period roughly) and you can not have conflicting components like one or two ports that depend on the old versions of PHP when everything else uses the current version of PHP. This is partly caused by pkg and its predecessor pkg_* tools but the origins of the restrictions are really in the very beginnings of the ports system.

You can't use portdowngrade here because this port isn't anymore in your port tree. The solution is to use svn, if I understand well your question. Here is an example with devel/e_dbus.

% portdowngrade devel/e_dbus
devel/e_dbus does not exist in /usr/ports

In a browser: Look in the commit history for the revision number you want (hang your mouse over the S image on the left of the line, in the date column). And look at the date you want. Here: 406189, 15 Jan 2016.
Then, I choose 2016Q1 (because of the date I want), then devel, OK, e_dbus is here.

In your home directory or where you want:
% svn co -r 406189 svn:// e_dbus-1.7.10_or_whatever_or_nothing

Then cd inside, make, sudo make deinstall install clean.

As noticed by others, this may be a bad idea… Good luck!