More power to grr!
grr now remembers the repositories found for the next execution. If you got a list of repositories, simply address them with :i (i is a number).
It is also possible to navigate to a repository with an index like grr cd :8
Additionally, grr remembers your last location so calling grr cd - will navigate back to the directory of the last grr-execution.
By the way, the - was inspired by git checkout - which takes you back to the last branch. Quite handy.