The V1 git man page had a reference about un-applying a stash. The excerpt is below.
The newer V2 git man page doesn't include any reference to un-applying a stash but the below still works well
Un-applying a Stash In some use case scenarios you might want to apply stashed changes, do some work, but then un-apply those changes that originally came from the stash. Git does not provide such a stash un-apply command, but it is possible to achieve the effect by simply retrieving the patch associated with a stash and applying it in reverse:
$ git stash show -p stash@{0} | git apply -R
Again, if you don’t specify a stash, Git assumes the most recent stash:
$ git stash show -p | git apply -R
You may want to create an alias and effectively add a stash-unapply command to your Git. For example:
$ git config --global alias.stash-unapply '!git stash show -p | git apply -R'
$ git stash apply
$ #... work work work
$ git stash-unapply