To resign old commits for git, just
git rebase --exec 'git commit --amend --no-edit -n -S' -i development
To make it easier,
resign = "!re() { git rebase --exec 'git commit --amend --no-edit -n -S' -i $1; }; re"
then
git resign HASH
See also https://superuser.com/questions/397149/can-you-gpg-sign-old-commits