1Dot what do you mean by "overridden"? If you are adding things to an ItemList using extend(), there shouldn't be any conflict as long as the extensions use unique names in the ItemList.
To influence the order in which things are added, the ItemList supports priorities (third argument to items.add(name, vnode, priority = 0).
If you need to change the order in which the extensions load, you can change the priority of the initializer (third argument to app.initializers.add(), or you can define another extension as a required or optional dependency of your own, so Flarum will make sure initializers with the same priority will run in the correct order https://docs.flarum.org/extend/extending-extensions.html#dependencies
Looking at the source code of your extension I don't see anything that might be causing an issue. Do you have a screenshot of which particular part of the interface gets overridden with something else?
