installing multiple copies of macports

[Marko Käning]

Section 2.3.4 (http://guide.macports.org/#installing.macports.source.multiple) of the manual explains how multiple macports installations can be created, but I cannot see a hint as to how these have to be set up in such a way that one can easily switch between these copies.

I can imagine that some services might get started for a specific macports installation, which would have to be shut down in some controlled manner before the alternative installation can be put into action.

Anyone out there who has such a setup actually in place and could give a hint?