of course the simplest method of reverting to an older binary is to just reactivate it if you still have it installed, but inactive, after an update.
This will show you what versions are installed: port -v installed portname and this: port activate portname will give you a menu of previous versions to activate. You may run into linkage troubles, etc, but I use this often to get out of a bind, where port X is updated but port Y that depends on it won't update and is now broken because of port X being updated. This buys me time to fix port Y and then update that in MacPorts, and then restore the current versions of everything. Ken
