modify gutenberg sidebar component?

I want to modify post excerpt sidebar component (
https://github.com/WordPress/gutenberg/blob/d0fa04737ffda96b03bade9d724bc7fd842482d4/packages/editor/src/components/post-excerpt/index.js)
I was able to modify it by adding javascript to post.php, but the problem is, that when you e.g. click the editor, so the sidebar tab switches from post to block and then go back to post tab, it is whole reinitialised and all my changes are gone. I would need a way, to either
a) modify the component, so that it will be always initialized with my changes (or delete this component and setup my version of it) or
b) run my modification script when the panel is inicialised