How to activate an older version of a port

[Jerry]

Hi list,

I'm trying to do a git bisection on LyX to find a problem. This is _not_ a macports build but done straight from the LyX repository. Newer versions build OK but on some somewhat older sources, I'm getting a complaint that only versions of automake 1.8 through 1.11 are supported, and I think this is causing the build to fail. Since /opt/local is seen before /usr/local/ (which has automake 1.9 in it), I want to temporarily roll back macports automake to 1.11.3. I get this:

$ port installed automake
The following ports are currently installed:
  automake @1.11.3_0
  automake @1.11.4_0
  automake @1.12_0
  automake @1.12.2_0
  automake @1.12.5_0 (active)

so it should be possible (right?) but I can't find the command to do this although I think I once saw it.

How can I activate an older version of automake and then re-activate the newest version later?

Thanks,
Jerry