如何从服务提供商中更改Laravel Container属性?

Laravel binds pathis into the Container like so

$this->instance('path.lang', $this->langPath());   

in bindPathsInContainer() in /vendor/laravel/framework/src/Illuminate/Foundation/Application.php I'd like to change this path from within my Service Provider to something else.

I know that the container instance is accessible through $this->app from within a Service Provider, and so thought I could do

$this->app->instance('path.lang', 'my/path');

This however returns "class instance does not exist." Can anyone explain what's going on here? Also, why does referencing ANY property of the container, as in

$this->app->someProperty

lead to this error? Is there a way to edit someProperty from within a service provider? NB: I know this can be done by extending \Illuminate\Foundation\Application, as explained here but I'd like to do this from without having to touch Laravel's default files.

I think the path has to be absolute:

php artisan tinker
app()->instance('path.lang', '/home/user/you/project/something/something/that/exists);

You can also try it like that in your AppServiceProvider:

$this->app->instance('path.lang', $this->app->resourcePath().DIRECTORY_SEPARATOR.'mylang');