XPLM_API int        XPLMEnablePlugin(
                         XPLMPluginID         inPluginID);    

This routine enables a plug-in if it is not already enabled. It returns 1 if the plugin was enabled or successfully enables itself, 0 if it does not. Plugins may fail to enable (for example, if resources cannot be acquired) by returning 0 from their XPluginEnable callback.