1. A computer program product, comprising a non-transitory computer usable medium having a computer readable program code embodied therein, the computer readable program code adapted to be executed to implement a method, the method comprising: creating, by a first user of an on-demand database service, a package definition that references a set of one or more metadata objects that describe an application, wherein the package definition includes: profile information defining at least one group of users allowed to access the application, user interface information defining a customization to a user interface; and a flag, set by the first user, to indicate that customization of the one or more metadata objects is allowed, distributing the one or more metadata objects for use by users of the on-demand database service: providing access to the customization to the user interface to the group of users allowed to access the application; and denying access to the customization to the user interface to other users not included in the group of users allowed to access the application.