Within an application you have the global node that can be accessed from anywhere in the app, but that is reset upon closing the app.
I think that if you want to have that kind of data upon another launch, you will have to use the roRegistry object.
https://sdkdocs.roku.com/display/sdkdoc/roRegistryWhen launching the app you could read from the registry and when an user sets another url you could save that in the registry.