Overriding plugin functionality in app

Good day, Grails and plugin developers,

I've encountered the following question when developing an app. I have a plugin and would like to override (expand) it functionality. How should it be done?

1. Is it possible to create the same class in app plugin folder? Whould it override the same class of the plugin?
2. Or the only way is to modify plugin code?

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Regards,
Alexei