Making the ship available to add in to a mission is the easy part, using modular table files. Changing each mission so that they will allow the user to fly that craft in a campaign is the hard part. That data is stored within a mission file (and campaign file sometimes) and there's no way to have the game automatically change all missions to make the new craft available. The only option available for you, would be to include with your modular table files, edited versions of all missions and campaign files for all campaigns you want the user to be able to fly the new craft in. You'd need to either have them all extracted to their proper folders to take prescedence over the mission files in the existing VPs, or combine the modular tables and edited missions into a drop-in VP file, which is named so that it will take prescendence over the other VPs.