For the necessary env changes we could adopt something like virtualenv's activate/deactive, i.e. `source ~/.dlang/dmd-2.069.0/activate` to use dmd-2.069.0. And of course we can activate the env after the download.
There is a pull request, try it out and provide feedback. https://trello.com/c/loy1eCRj/136-install-script https://github.com/D-Programming-Language/installer/pull/162
