redo destroot after tweaking build?

["René J.V. Bertin"]

Suppose one is working on adapting an OS project to become a port. You've done a `port destroot` and then realise you want to try some small change in the build. Rather than doing the whole build all over again, you do a `make` in the build directory ... and then what? I just discovered that removing the destroot directory isn't enough to let `port destroot` create a new one, which leaves me in a bit of a deadlock situation.
Help?

R.