No, the init.d/openvpn script always start at the bootup. However it has a variable that can be wrote to signal wether you want to start the daemons or not.
This is the varaible AUTOSTART and its value could be 'ALL', 'NONE' or the names of the openvpn daemons to activate.
You can write a short script that edits this value in the file (with sed for example) and starts or stops the service.
As last thing, remember when changing package files that the package's upgrade we will overwrite any custom changes, so take care of this.