Unable to use outside variables inside a parameter defined as function

[AdrielD]

I'm developing an addon to dynamically change the components' styles (they are built as web components with LitElement).
The code below does not work (the message does not get printed) because of the external variables (Button and buttonStyles). If I remove that line, "ahoy!" gets printed into the console.

import Button from './index.js';
import buttonStyles from './styles.js';

export default {
  title: 'Components/Button',
  argTypes: {
    text: { control: 'text' },
    disabled: { control: 'boolean' },
  },
  parameters: {
    brandchanger: {
      definestyle: (brandName) => {
        console.log("ahoy!");
        Button.styles = buttonStyles(brandName);
      },
    },
  }
};

Even a simple variable causes the function to not execute:

const a = 123;

export default {
  ...
  parameters: {
    brandchanger: {
      definestyle: (brandName) => {
        console.log(a); <--- does not recognize variable, despite it being declared at the same story file, and higher level context
      },
    },
  }
};

Is that by design? Is it possible to make the parameters understand an outside variable, or, better yet, a callback that the addon can receive to execute when it finished loading