Manually stepping through port phases

[Scott Webster]

Looking for some pointers for sequentially stepping through the
different port phases... The reason I want to do this is to test a
change to a package (modify the source), so I figured I would do the
following:

port fetch gimp2
port extract gimp2
*make my changes*
port patch gimp2
port configure gimp2
port build gimp2
port destroot gimp2
port install gimp2
port activate gimp2

It looks like what happened is that everything was fine up until the
"port install" command and it seems that then port decided I didn't
need to install after all and wiped out the destroot through it's
cleaning process.  This is likely because I already have gimp2
installed I guess... but is there a way to make "port install" only do
the "install" phase (as defined in the macports guide as "Copy a
port's destrooted files into ${prefix}/var/macports/software.")?

"port activate" then failed with:
[~@swmb]$ sudo port -v activate gimp2
sudo: cannot get working directory
shell-init: error retrieving current directory: getcwd: cannot access
parent directories: No such file or directory
error getting working directory name: no such file or directory
    while executing
"pwd"
    invoked from within
"set current_portdir [pwd]"
    (file "/opt/local/bin/port" line 4381)

Probably what I should really be doing though is somehow making my own
variant and then installing that, such that I can switch back and
forth between versions easily...

Scott