Plugin SDK can be used with existing Five9 Integrations if CRM system allow embedding custom javascript code inside web pages. When customizing existing integrations developers can use all InteractionApi methods and callbacks InteractionApiEvents, HookApi methods and callbacks HookApiCallbacks. CrmApi is not available as in this case Five9 is providing its own implementation of basic CRM integration functionality.
In order to customize existing integrations developers must load Five9 Plugin SDK javascript library using method for loading 3rd party javascript provided by specific CRM system. Once library is loaded it will automatically discover Five9 Adapter.
Five9 Plugin SDK can be loaded in multiple iframes within the same page and in multiple pages running in different browser tabs. All instances of the library will get InteractionApiEvents callbacks executed upon appropriate events. You can use isMasterPage method if some operations need to be executed only once.
There are examples of using Five9 Plugin SDK library with CRM systems which has been tested for compatibility.