1. A method for use in modifying program content, comprising the steps of: identifying locations in the content where dynamically replaceable assets can be inserted; establishing dynamically replaceable assets in one or more of the identified locations in the content; determining location information for each established dynamically replaceable asset; determining visual effects information associated with each established dynamically replaceable asset; and creating a reference file that includes the location and the visual effects information associated with each established dynamically replaceable asset.