To add a local plugin with ionic :
ionic cordova plugin add /path/to/my/plugin/my.plugin.folder.here/
to remove it :
ionic cordova plugin remove my.plugin.folder.here
But to update it it’s another problem. Actually I’m removing and installing it again after each edit. Good luck 😉
EDIT
If you are using a previous version of ionic cli, and it doesn’t work, change the commands to the following :
ionic plugin add /path/to/my/plugin/my.plugin.folder.here/
and
ionic plugin remove my.plugin.folder.here