Is adding methods to a plugin's API a "good" way?

Hi there. I altered the autogrow-plugin so the bug where the instance loses focus in Safari when the editor resizes and added an animation to the resizing. I need to trigger the resizing from 'outside' the editor while passing it a parameter (the duration of the resize-animation). Now I was wondering if it's a good, clean way to just add a public method to where the init-method is defined so I can call

my_editor_instance.plugins.my_autogrow.resize();

or if there is another, right way to do this.

Thanks in advance
Luke