1. A system comprising: a network interface configured to enable communication with computing devices via a network; and a content package creator configured to: receive, via the network interface, user input from a plurality of the computing devices on which respective instances of a program execute, the user input identifying content of the program to update and defining one or more content updates of user-defined content; assemble the one or more content updates of user-defined content that correspond with the identified content into a package of content updates that is suitable for transmission over the network; and transmit, via the network interface, the package of content updates to another of the computing devices on which another instance of the program executes effective to cause the other instance of the program to implement the one or more content updates to replace the identified content with the user-defined content.