The OPC UA Complex Data extension is enabled by default.
Disabling the Complex Data plug-in may be useful e.g. for licensing reasons (when the product edition you have does not support the Complex Data plug-in, and you want to avoid the associated error), or for performance reasons (if you do not need the internal content of the value, for example if your code just needs to take the value read, and write it elsewhere).
Enabling or disabling the OPC UA Complex Data extension is done by settings the Enabled Property in the PluginSetup for the extension. You can locate the PluginSetup in the PluginSetups Property of the InstanceParameters of EasyUAClient. In order to find the proper PluginSetup, call the FindName Method on the PluginSetupCollection Class, giving it "UAComplexDataClient" string as an argument, or search the PluginSetups for a PluginSetup that has its UriString Property equal to EasyOpcUAUriStrings.ComplexDataClientPlugin.
When the OPC UA Complex Data extension is disabled, the component
When the OPC UA Complex Data extension is enabled (the default) but the current license does not allow the OPC UA Complex Data feature, reads, subscriptions and writes, or attempts to obtain services related to OPC UA Complex Data, will return an error.