Beyond updating to the specific git-hashes you want every time (or tracking #head as you do) I can't think of anything.
If it's something that occurs often, maybe making a nimble-task out of it might
be useful?
task reinstall, "Installs this package and ensures a redownload of the
emailparser's most recent commit":
rm -rf ~/.nimble/pkgs2/emailparser-0.1.0-*
nimble install -d
Run
Then you can just `nimble reinstall` instead of having to always do it manually
