1. A method comprising: providing a computing system; displaying, by the computing system, a customized user interface (UI) component, the customized UI component being a version of a UI component to which client customizations have been applied, the UI component being a component of a UI of an application, wherein a customized interface definition defines the customized UI component; modifying a solution set, the solution set comprising one or more solutions that modify the UI component, and modification including adding a new solution to the solution set, wherein adding the new solution to the solution set comprises: receiving a change list that specifies changes; generating a new non-customized interface definition by applying applicable changes to a non-customized interface definition, the non-customized interface definition being an interface definition that defines a version of the UI component that results from applying the modifications provided by each solution in the solution set to a base version of the UI component; and after applying the applicable changes to the non-customized interface definition, generating a new customized interface definition by applying changes in a customization change list to the new non-customized interface definition, the customization change list expressing the client customizations, the new customized interface definition defining a new customized UI component; and after the solution set is modified, displaying, by the computing system, the new customized UI component, the new customized UI component being a version of the UI component to which modifications provided by solutions in the solution set are applied and to which the client customizations remain applied to the UI component, the client customizations remaining applied to the UI component without manually re-applying the client customizations to the UI component.