There's no easy way to edit system/local using the deployment server. You will have to manually delete the inputs.conf and outputs.conf files from system/local and point your forwarder to your deployment server (by editing the deploymentclient.conf file) and restarting Splunk.
From there, you can edit the serverclass.conf file on your deployment server (which will store all of the names of your servers which has forwarders on them.)
Then you can create a simple app in etc/deployment-apps consisting of an inputs.conf and outputs.conf file (similar to what you already had on your forwarder, but you will be able to control this remotely without messing around with the forwarder).
To make sure the forwarder uses IP address, use connection_host=IP as an option for your [WinEventLog:Security] stanza in the inputs.conf file in your app.
Once the app has been created, you will use the "splunk reload deploy-server" command to send the app to your forwarder.
... View more