Shouldn't you use onAfterRoute instead ?

onAfterInitialise() is called before onAfterRoute().

The onAfterRoute has already loaded the non-desired view/component

I don't know how onAfterRoute has already loaded the non-desired view/component. On my quick test, I used the code like this:

public function onAfterRoute()
{
	if ($this->app->isClient('site'))
	{
		$this->app->input->set('option', 'com_contact');
		$this->app->input->set('view', 'category');
		$this->app->input->set('id', 4);
		$this->app->input->set('layout', 'default');
	}

}

And that loads category view of category with ID = 4 in com_contact. So onAfterRoute() works well for me. I can use that event to route to the component/view I want.

On Joomla 1.5 up to 3.x the onAfterInitialise() worked for me.

I don't know if has any issue the specific component I am trying (virtuemart)

I will do my tests and I will come back with the results

I will have to check it again but I remember I read somewhere that in Joomla 3, Joomla Input object use $_REQUEST as reference, so any modification to Joomla input object will affect data from $_REQUEST.

On Joomla 4, $_REQUEST is not passed by reference to input object anymore, so modify Joomla input object won't make change to $_REQUEST.

With that said, if VM for some reasons, uses data from $_REQUEST instead of using data from Joomla input object, the change won't have any affect.

(Haven't looed at VM from long time ago, so I can just guess)

As for modify routing variables like in this example, I believe onAfterRoute is the right event to use.

Hope you will figure out and come up with a solution.

Closing because this is a none core issue. Feel free to re-open if you have something want to discuss further.