Sometimes I have to respin a patch-serie to address some new concerns. This time was a little bit more difficult: I first thought the a new feature can be applied on top of HEAD, later I realized that this particular feature should be applied on a previous commit. The workflow with git is really easy:

# save changes in stash stack
git stash

# start to rewrite history
# change the addressed patch to 'edit' 
git rebase --interactive HEAD

# re-apply the changes
git stash pop

# eventually fix merge commits
vim file-to-fix.c
git add file-to-fix.c

# recommit
git commit --amend

# finish rebasing
git rebase --continue