I add it on PAGE_CONTAINER template, is that okay?
		
		
	 
This might or might not work, depending on where you want to access the param.
XenForo template engine works like this:
The template to be used is defined in the controller by code like
	
	
	
		PHP:
	
	
		return $this->view($viewClass, $viewTemplate, $viewParams);
	 
 
The defined template 
$viewTemplate (which might be smth. like 
thread_view does get rendered and while it is being rendered, all sub-templates/macros do get included.
Afterwards, template 
PAGE_CONTAINER does get rendered which does get the HTML of the rendered template as variable 
$content.
While rendering 
PAGE_CONTAINER, other templates (like the one for ad position 
container_header) do get included.
So if you define a page param right at the top of PAGE_CONTAINER you can use it in templates that are included by PAGE_CONTAINER; however you can't use it in templates like 
thread_view (and templates included by those templates) as those are rendered before rendering of 
PAGE_CONTAINER has started.
So for your specific question if depends on the ad location where you would to use the param:
- container_breadcrumb_top_above
 
- container_breadcrumb_top_below
 
- container_header
 
- container_sidenav_above
 
- container_sidenav_below
 
- container_content_above
 
- container_content_below
 
- container_sidebar_above
 
- container_sidebar_below
 
- container_breadcrumb_bottom_above
 
- container_breadcrumb_bottom_below
 
would work - others (eg. those within specific  templates) would not.
A generic approach purely with templates that should always work:
Create a template 
my_node_ids
	
	
	
		Code:
	
	
		<xf:page option="publicNodeIds" value="{{ [1, 2, 3] }}" />
<xf:page option="privateNodeIds" value="{{ [4, 5, 6] }}" />
<xf:page option="optionalNodeIds" value="{{ [7, 8, 9] }}" />
	 
 
and include this everywhere you need your checks like
	
	
	
		Code:
	
	
		<xf:include template="my_node_ids" />
	 
 
Afterwards you could use conditions like
	
	
	
		Code:
	
	
		<xf:if is="in_array($__globals.forum.node_id, page_param('publicNodeIds'))">
	 
 
Though this isn't terribly efficient and kinda hacky, using an Add-on would be cleaner
You could also just use a configuration array in config.php
	
	
	
		PHP:
	
	
		$config['rdn_publicNodeIds'] = [1, 2, 3];
	 
 
This could be accessed in any templates via
	
	
	
		Code:
	
	
		<xf:if is="in_array($__globals.forum.node_id, $xf.app.config.rdn_publicNodeIds)">