Some Sibelius plugins (for example, Respell Sharps as Flats) run without taking any input from a user. They do not display a dialog, but just run and do what they were designed to do.
Other plugins take input from users by putting up a dialog box that has boxes to type into, or check boxes, list boxes, or radio buttons. You might see a dialog that looks like this:

In this dialog there is a great deal of data, but the initial values in the edit boxes will change every time the plugin is run, because they are pulled out of the current score. The plugin does not save anything from the previous run, but instead always starts fresh.
Other plugins, however, remember what a user typed in the last time the plugin was run, assuming that the same settings might be used again. Here are some different ways plugins can save these settings.
 more >> “How Sibelius Plugins Store their Settings for User Data”