Generally speaking, you really don't want to insert anything into the MediaVPs or a mod's VP files; that almost inevitably winds up causing support nightmares at some point down the road. Instead, what you want to do is add the model and its associated files to a particular mod's data folder, since files in the data folder override any identically-named files in a VP file. The path would generally look like FreeSpace2\*modname*\data\models for the actual model file, and \data\maps or \data\tables\ for the associated texture and table files, if any. Depending on how you want to set things up, you could put the model in the mod folder for the FSPort MediaVPs, so that it would override any instance of the Apollo in a Port campaign.
